A^8093^Arbuscular mycorrhizae, ubiquitous mutualistic symbioses between plant roots and fungi in the order Glomales, are believed to be important controllers of plant responses to global change, in particular to elevated atmospheric CO2. In order to test if any effects on the symbiosis can persist after long-term treatment, we examined root colonization by arbuscular mycorrhizal (AM) and other fungi of several plant species from two grassland communities after continuous exposure to elevated atmospheric CO2 for six growing seasons in the field. For plant species from both a sandstone and a serpentine annual grassland there was evidence for changes in fungal root colonization, with changes occurring as a function of giant host species. We documented decreases in percentage nonmycorrhizal fungal root colonization in elevated CO2 for several plant species. Total AM root colonization (%) only increased significantly for one out of the five plant species in each grassland. However, when dividing AM fungal hyphae into two groups of hyphae (fine endophyte and coarse endophyte), we could document significant responses of AM fungi that were hidden when only total percentage colonization was measured. We also documented changes in elevated CO2 in the percentage of root colonized by both AM hyphal types simultaneously. Our results demonstrate that changes in fungal root colonization can occur after long-term CO2 enrichment, and that the level of resolution of the study of AM fungal responses may have to be increased to uncover significant changes to the CO2 treatment. This study is also one of the first to document compositional changes in the AM fungi colonizing roots of plants grown in elevated CO2. Although it is difficult to relate the structural data directly to functional changes, possible implications of the observed changes for plant communities are discussed.

2669^2^Zaller,J G^Arnone,J A^1999^1^Earthworm responses to plant species' loss and elevated CO2 in calcareous grassland^206^208^1^1-8^^^^^^^^^^8096hyphae 1787^2467^2516^3744^407^427^672^ndophyte and coarse endophyte), we could document significant responses of AM fungi that were hidden when only total percentage colonization was measured. We also documented changes in elevated CO2 in the percentage of root colonized by both AM hyphal types simultaneously. Our results demonstrate that changes in fungal root colonization can occur after long-term CO2 enrichment, and that the level of resolution of the study of AM fungal responses may have to be increased to uncover significant changes to the CO2 treatment. This study is also one of the first to document compositional changes in the AM fungi colonizing roots of plants grown in elevated CO2. Although it is difficult to relate the structural data directly to functional changes, possible implications of the observed changes for plant communities are discussed.

2669^2^Zaller,J G^Arnone,J A^1999^1^Earthworm responses to plant species' loss and elevated CO2 in calcareous grassland^206^208^1^1-8^^^^^^^^^^8096hyphae A^8095^The objectives of this study were: (1) to quantify the effects of plant species' loss from designed calcareous grassland communities at a field site in northwestern Switzerland on the size and composition of earthworm communities, and (2) to evaluate how exposure of plant communities to elevated atmospheric CO2 might alter the effects of plant species' loss on earthworm communities. We non-destructively censused earthworm communities in each of 24 1.2 m(2) experimental plots in autumn 1996 when soils were wet and earthworms were active. Each plot contained an experimental plant community with 31, 12 or 5 native plant species (eight plots each). Half of the plots in each species treatment were exposed to ambient CO2 concentrations (350 mu L CO2 L-1) and half to elevated CO2 (600 mu L CO2 L-1) using screen-aided CO2 control. The study was conducted in the fourth year after community establishment and the third year of CO2 treatment as part of a long-term study on the interactive effects of plant species' loss and elevated CO2 on grassland communities. The size (density and biomass) of earthworm communities declined linearly when the number of plant species in the community was reduced from 31 to 5 species (e.g. 32 +/- 1 g m(-2) to 23 +/- 2 g m(-2)) due mainly to a decline in the endogeic worm species Allolobophora rosea which was the most abundant of nine earthworm species observed (nearly half of all worms in each plot). However, no changes in the relative contribution of individual species or the three main earthworm ecological groups (anecics, endogeics, epigeics) to the entire earthworm community were observed with declining number of plant species. The responses of earthworm communities to plant species' loss appear to reflect changes in community fine root biomass in the topsoil (e.g. declining worm biomass with declining fine root biomass) observed in parallel studies conducted at this site. Further the results of this study demonstrate that a loss of plant species' from these calcareous grassland communities may also alter the age structure of earthworm communities, but not significantly influence their diversity or composition. Our data also indicate that rising atmospheric CO2 may not greatly impact the size and composition of worm communities or alter the effects of plant species' loss on earthworm communities. Therefore, the disappearance of plant species from these native grasslands, as a result of ever increasing human activities, may be expected to lead to reductions in the size of earthworm communities and the ecosystem services they provide.

2670^4^Nguyen,Q T^Kozai,T^Niu,G^Nguyen,U V^1998^1^Photosynthetic characteristics of coffee (Coffea arabusta) plantlets in vitro in response to different CO2 concentrations and light intensities^177^55^2^133-139^^^^^^^^^^8098
781^il (e.g. declining worm biomass with declining fine root biomass) observed in parallel studies conducted at this site. Further the results of this study demonstrate that a loss of plant species' from these calcareous grassland cA^8097^The photosynthetic characteristics of coffee (Coffea arabusta) plantlets cultured in vitro in response to different CO2 concentrations inside the culture vessel and photosynthetic photon flux (PPF) were investigated preliminarily. The estimation of net photosynthetic rate (P-n) of coffee plantlets involved three methods: (1) estimating time courses of actual P-n in situ based on measuring CO2 concentrations inside and outside the vessel during a 45-day period, (2) estimating P-n in situ at different CO2 concentrations and PPFs using the above measuring approach for 10-day and 30-day old in vitro plantlets, and (3) estimating P-n of a single leaf at different CO2 concentrations and PPFs by using a portable photosynthesis measurement system for 45-day old in vitro coffee plantlets. The results showed that coffee plantlets in vitro had relatively high photosynthetic ability and that the P-n increased with the increase in CO2 concentration inside the vessel. The CO2 saturation point of in vitro coffee plantlets was high (4500-5000 mu mol mol(-1)); on the other hand, the PPF saturation point was not so high as compared to some other species, though it increased with increasing CO2 concentration inside the vessel.





2672^4^Harwood,K G^Gillon,J S^Roberts,A^Griffiths,H^1999^1^Determinants of isotopic coupling of CO2 and water vapour within a Quercus petraea forest canopy^2^119^1^109-119^^^^^Apr^^^^^8102
1533^1853^1859^312^344^3745^3746^3747^3748^393^ a 45-day period, (2) estimating P-n in situ at different CO2 concentrations and PPFs using the above measuring approach for 10-day and 30-day old in vitro plantlets, and (3) estimating P-n of a single leaf at different CO2 concentrations and PPFs by using a portable photosynthesis measurement system for 45-day old in vitro coffee plantlets. The results showed that coffee plantlets in vitro had relatively high photosynthetic ability and that the P-n increased with the increase in CO2 concentration inside the vessel. The CO2 saturation point of in vitro coffee plaA^8101^Concentration and isotopic composition (delta(13)C and delta(18)O) of ambient CO2 and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for delta(a) (CO2)-C-13, delta(a) (COO)-O-18-O- 16 and delta(a) (H2O)-O-18, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. delta(13)C of organic matter input for delta(a) (CO2)-C-13 delta(18)O Of exchangeable water for delta(a) (COO)-O-18-O-16 and transpired water vapour for delta(a) (H2O)-O-18. [CO2] and delta(a) (CO2)- C-13 showed strong coupling, where the released CO2 was, on average, 4 per mil enriched compared to the organic matter of plant material in the system? suggesting either fractionation of organic material before eventual release as soil-respired CO2, or temporal differences in ecosystem discrimination. delta(a) (COO)-O-18-O-16 was less well coupled to [CO2], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, delta(a) (H2O)-O-18 was less coupled to [H2O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The delta(18)O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO2 and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time.
ionation of organic material before eventual release as 2673^2^Refouvelet,E^Daguin,F^1999^1^Polymorphic glutamate dehydrogenase in lilac vitroplants as revealed by combined preparative IEF and native PAGE: Effect of ammonium deprivation, darkness and atmospheric CO2 enrichment upon isomerization^37^105^2^199-206^^^^^Feb^^^^^8104
1538^2346^3749^3750^385^472^756^ecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The delta(18)O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO2 and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time.
ionation of organic material before eventual release as A^8103^The activity and polymorphism of glutamate dehydrogenase (GDH) were studied in basal callus of Lilac (Syringa eulgaris L.) vitroplants. Native PAGE alone revealed seven bands staggered at regular intervals. Preparative liquid-vein IEF allowed the separation of six to ten GDH fractions with charges ranging between 5.18 and 7.08. Analysis of these GDH fractions in native PAGE indicated that up to seven GDH bands can be detected for each fraction. This suggests the existence of seven isoforms of the enzyme with subunits presenting different isoelectric points. Dark- and ammonium-controlled forms were found to be the more acidic and faster migrating ones in native PAGE. The results support for the first time that atmospheric CO2 enrichment increases GDH activity dramatically and modifies isomerization of the enzyme.

2674^3^Lee,H Y^Chow,W S^Hong,Y N^1999^1^Photoinactivation of photosystem II in leaves of Capsicum annuum^37^105^2^377-384^^^^^Feb^^^^^8106
1092^188^2047^2219^3751^3752^3753^3754^434^763^ as A^8105^Leaf discs of Capsicum annuum L. were illuminated in air enriched with 1% CO2 in the absence or presence of lincomycin, an inhibitor of chloroplast-encoded protein synthesis. The loss of functional photosystem (PS) II complexes with increase in cumulative light dose (photon exposure), assessed by the O-2 yield per single-turnover flash, was greater in leaves of plants grown in low light than those in high light; it was also exacerbated in the presence of lincomycin. A single exponential decay can describe the relationship between the loss of functional PSII and increase in cumulative photon exposure. From this relationship we obtained both the maximum quantum yield of photoinactivation of PSII at limiting photon exposures and the coefficient k, interpreted as the probability of photoinactivation of PSII per unit photon exposure. Parallel measurements of chlorophyll fluorescence after light treatment showed that 1/F-o--1/F-m was linearly correlated with the functionality of PSII, where F-o and F-m are the chlorophyll fluorescence yields corresponding to open and closed PSII reaction centers, respectively. Using 1/F-o--I/F-m as a convenient indicator of PSII functionality, it was found that PSII is present in excess; only after tbe loss of about 40% functional PSII complexes did PSII begin to limit photosynthetic capacity in capsicum leaves.

2675^1^Idso,S B^1999^1^The long-term response of trees to atmospheric CO2 enrichment^127^5^4^493-495^^^^^Apr
417^92^
2676^3^Midgley,G F^Wand,S J E^Pammenter,N W^1999^1^Nutrient and genotypic effects on CO2-responsiveness: Photosynthetic regulation in Leucadendron species of a nutrient-poor environment^78^50^333^533-542^^^^^Apr^^^^^8109
1262^130^2346^360^3755^3756^376^714^733^953^xposures and the coefficient k, interpreted as the probability of photoinactivation of PSII per unit photon exposure. Parallel measurements of chlorophyll fluorescence after light treatment showed that 1/F-o--1/F-m was linearly correlated with the functionality of PSII, where F-o and F-m are A^8108^Four South African Leucadendron congenerics with divergent soil N and P preferences were grown as juveniles at contrasting nutrient concentrations at ambient (350 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) atmospheric CO2 levels. Photosynthetic parameters were related to leaf nutrient and carbohydrate status to reveal controls of carbon uptake rate. In ail species, elevated CO2 depressed both the maximum Rubisco catalytic activity (V-c,V-max, by 19-44%) and maximum electron transport rate (J(max) by 13-39%), indicating significant photosynthetic acclimation of both measures. Even so, all species had increased maximum light-saturated rate of net CO2 uptake (A(max)) at the elevated growth CO2 level, due to higher intercellular CO2 concentration (c(i)). Leaf nitrogen concentration was central to photosynthetic performance, correlating with A(max), V-c,V-max and J(max). V-c,V-max and J(max) were linearly cc-correlated, revealing a relatively invariable J(max):V-c,V-max ratio, probably due to N resource optimization between light harvesting (RuBP regeneration) and carboxylation. Leaf total non-structural carbohydrate concentration (primarily starch) increased in high CO2, and was correlated with the reduction in V-c,V-max and J(max). Apparent feedback control of V-c,V-max and J(max) was thus surprisingly consistent across all species, and may regulate carbon exchange in response to end-product fluctuation. If so, elevated CO2 may have emulated an excess end-product condition, triggering both V-c,V-max and J(max) down-regulation. In Leucadendron, a general physiological mechanism seems to control excess carbohydrate formation, and photosynthetic responsiveness to elevated CO2, independently of genotype and nutrient concentration. This mechanism may underlie photosynthetic acclimation to source:sink imbalances resulting from such diverse conditions as elevated CO2, low sink strength, low carbohydrate export, and nutrient limitation.
 a relatively invariable J(max):V-c,V-max ratio, probably due to N reso2677^10^Kimball,B A^LaMorte,R L^Pinter,P J^Wall,G W^Hunsaker,D J^Adamsen,F J^Leavitt,S W^Thompson,T L^Matthias,A D^Brooks,T J^1999^1^Free-air CO2 enrichment and soil nitrogen effects on energy balance and evapotranspiration of wheat^133^35^4^1179-1190^^^^^Apr^^^^^8111
1494^2712^341^344^3757^3758^3759^3760^442^508^istent across all species, and may regulate carbon exchange in response to end-product fluctuation. If so, elevated CO2 may have emulated an excess end-product condition, triggering both V-c,V-max and J(max) down-regulation. In Leucadendron, a general physiological mechanism seems to control excess carbohydrate formation, and photosynthetic responsiveness to elevated CO2, independently of genotype and nutrient concentration. This mechanism may underlie photosynthetic acclimation to source:sink imbalances resulting from such diverse conditions as elevated CO2, low sink strength, low carbohydrate export, and nutrient limitation.
 a relatively invariable J(max):V-c,V-max ratio, probably due to N resoA^8110^In order to determine the likely effects of the increasing atmospheric CO, concentration on future evapotranspiration, ET, plots of field-grown wheat were exposed to concentrations of 550 mu mol/mol CO2 (or 200 mu mol/mol above current ambient levels of about 360 mu mol/mol) using a free-air CO2 enrichment (FACE) facility. Data were collected for four growing seasons at ample water and fertilizer (high N) and for two seasons when soil nitrogen was limited (low N). Measurements were made of net radiation, R-n; soil heat flux; air and soil temperatures; canopy temperature, T-s; and wind speed. Sensible heat flux was calculated from the wind and temperature measurements. ET, that is, latent heat flux, was determined as a residual in the energy balance. The FACE treatment increased daytime T-s about 0.6 degrees and 1.1 degrees C at high and low N, respectively. Daily total R-n was reduced by 1.3% at both levels of N. Daily ET was consistently lower in the FACE plots, by about 6.7% and 19.5% for high and low N, respectively.

2678^3^Musil,C F^Midgley,G F^Wand,S J E^1999^1^Carry-over of enhanced ultraviolet-B exposure effects to successive generations of a desert annual: interaction with atmospheric CO2 and nutrient supply^127^5^3^311-329^^^^^Mar^^^^^8113
1432^341^3536^372^3761^3762^3763^715^953^965^CO2 enrichment (FACE) facility. Data were collected for four growing seasons at ample water and fertilizer (high N) and for two seasons when soil nitrogen was limited (low N). Measurements were made of net radiation, R-n; soil heat flux; air and soil temperatures; canopy temperature, T-s; and wind speed. Sensible heat flux was calculated from the wind and temperature measurements. ET, that is, latent heat flux, was determined as a residual in the energy balance. The FACE treatment increased daytime T-s about 0.6 degrees and 1.1 degrees C at high and low N, respectively. Daily total R-n was reduced by 1.3% at both levels of N. Daily ET was consistently lower in the FACE plots, by about 6.7% and 19.5% for high and lA^8112^The performance of fifth generation offspring of a desert annual (Dimorphotheca sinuata DC.) were compared in the absence of UV-B, under variable atmospheric CO2 and nutrient supply after four consecutive generations of concurrent exposure of their progenitors to UV-B at ambient (seasonal range: 2.55-8.85 kJ m(-2) d(-1)) and enhanced (seasonal range: 4.70-11.41 kJ m-2 d(-1)) levels. Offspring of progenitors grown under elevated UV-B exhibited a diminished photosynthetic rate, a consequence of a reduced leaf density, and diminished foliar levels of carotenoids, polyphenolics and anthocyanins. Conversely nonstructural carbohydrate and chlorophyll b levels were increased. Altered physiology was accompanied by reduced apical dominance and earlier flowering, features generally considered under photomorphogenic control, increased branching and inflorescence production and greater partitioning of biomass to reproductive structures, but diminished seed production. Many of these changes were magnified under nutrient limitation and intensified under atmospheric CO2 enriched conditions. The latter disagrees with current opinion that elevated CO2 may reduce detrimental UVB effects, at least over the long-term. Observed correlations between seed production and polyphenolic, especially anthocyanin, levels in offspring, and indications of diminished lignification (thinner leaves, less robust stems and fewer lignified seeds set) all pointed to the involvement of the phenylpropanoid pathway in seed formation and plant structural development and its disruption during long-term UV-B exposure. Comparisons with earlier generations revealed trends with cumulative generations of enhanced UVB exposure of increasing chlorophyll b and nonstructural carbohydrates, decreasing polyphenolics and biomass allocation to vegetative structures, and diminishing seed production despite increasing biomass allocation to reproductive structures. Notwithstanding some physiological compensation (increased chlorophyll b), the accumulation and persistence of these ostensibly inherited changes in physiological and reproductive performance suggest a greater impact of elevated UV-B on vegetation, primary production and regeneration over the long-term than presently envisaged.

2679^5^Chen,K^Ha,G Q^Keutgen,N^Janssens,M J J^Lenz,F^1999^1^Effects of NaCl salinity and CO2 enrichment on pepino (Solanum muricatum Ait.) - I. Growth and yield^165^81^1^25-41^^^^^29 Apr^^^^^8115
1460^243^312^344^374^417^672^948^nylpropanoid pathway in seed formation and plant structural development and its disruption during long-term UV-B exposure. Comparisons with earlier generations revealed trends with cumulative generations of enhanced UVB exposure of increasing chlorophyll b and nonstructural carbohydrates, decreasing polyphenolics and biomass allocation to vegetative structures, and diminishing seed production despite increasing biomass allocation to reproductive structures. Notwithstanding some physiological compensation (increased chlorophyll b), the accumulation and perA^8114^One-month old, rooted, semi-hardwood cutting plants of pepino cv. Xotus in sand-potted culture were treated with 200 mi Hoagland nutrient solution with or without additional 25 mM NaCl twice a week for 2 months, and exposed to 350 +/- 10, 700 +/- 10 or 1050 +/- 10 ppm CO2 in controlled environment chambers during the last month of the experiment. NaCl salinity in the rhizosphere reduced growth of all the organs, but raised stem dry weight ratio and root dry weight ratio. In contrast, atmospheric CO2 enrichment increased plant and fruit growth. Leaf dry weight ratio and fruit dry weight ratio rose, but stem dry weight ratio and root dry weight Patio decreased at high CO2 levels. Daily expansion rate of leaf area, growth rate of side-shoot length, rate of plant dry mass production, and increased rate of fresh fruit weight decreased due to NaCl stress, but increased with CO2 enrichment. Side-shoot diameter rose, whereas specific leaf area, leaf area ratio, and side- shoot dry weight ratio declined under both NaCl-stressed and CO2-enriched conditions. In comparison with the 350 ppm CO2 treatment without NaCl salinity in the rhizosphere, net assimilation rate and relative growth rate of plants were reduced by 8-13% and 16-32% due to NaCl salinity, and enhanced by 22-23% and 42-64% at 700 ppm CO2, and by 36-44% and 64-101% at 1050 pm CO2, respectively. The simultaneous treatments of NaCl salinity and high CO2 resulted in indefinite effects on vegetative and reproductive growth as well as on dry mass production of different plant organs. Nevertheless, the negative impacts of NaCl stress on plant growth and fruit yield diminished at high CO2 levels. Atmospheric CO2 enrichment increased the tolerance of pepino to NaCl salinity in the root medium. (C) 1999 Elsevier Science B.V. All rights reserved.

2680^1^Fearnside,P M^1999^1^Plantation forestry in Brazil: the potential impacts of climatic change^310^16^2^91-102^^^^^^^^^^8117
1927^427^c leaf area, leaf area ratio, and side- shoot dry weight ratio declined under A^8116^Most climatic changes predicted to occur in Brazil would reduce yields of silvicultural plantations, mainly through increased frequency and severity of droughts brought on by global warming and by reduction of water vapor sources in Amazonia caused by deforestation. Some additional negative effects could result from changes in temperature, and positive effects could result from CO2 enrichment. The net effects would be negative, forcing the country to expand plantations onto less-productive land, requiring increased plantation area land consequent economic losses) out of proportion to the climatic change itself. These impacts would affect carbon sequestration and storage consequences of any plans for subsidizing silviculture as a global warming mitigation option. Climate change can be expected to increase the area of plantations needed to supply projected internal demand for and exports of end products from Brazil. June-July-August (dry season) precipitation reductions indicated by simulations reported by the Intergovernmental Panel on Climate Change (IPCC) correspond to rainfall declines in this critical season of approximately 34% in Amazonia, 39% in Southern Brazil and 61% in the Northeast. As an example, if rainfall in Brazilian plantation areas (most of which are now in Southern Brazil) were to decline by 50%, the area needed in 2050 would expand by an estimated 38% over the constant climate case, bringing the total plantation area to 4.5 times the 1991 area. These large areas of additional plantations imply substantial social and environmental impacts. Further addition of plantation area as a global warming response option would augment these impacts, indicating the need for caution in evaluating carbon sequestration proposals. (C) 1999 Elsevier Science Ltd. All rights reserved.

2681^4^Bellisario,L M^Bubier,J L^Moore,T R^Chanton,J P^1999^1^Controls on CH4 emissions from a northern peatland^137^13^1^81-91^^^^^Mar^^^^^8119
1234^1377^1534^3764^3765^3766^3767^416^429^86^dicated by simulations reportedA^8118^We examined the controls on summer CH4 emission from five sites in a peatland complex near Thompson, Manitoba, Canada, representing a minerotrophic gradient from bog to rich fen at wet sites, where the water table positions ranged from -10 to - 1 cm. Average CH4 flux, determined by static chambers on collars, ranged from 22 to 239 mg CH4-C m(-2) d(-1) and was related to peat temperature. There was an inverse relationship between water table position and CH4 flux: higher water tables led to smaller fluxes. The determination of anaerobic CH4 production and aerobic CH4 consumption potentials in laboratory incubations of peat samples was unable to explain much of the variation in CH4 flux. Average net ecosystem exchange of CO2 ranged from 1.4 to 2.5 g CO2-C m(-2) d(-1) and was strongly correlated with CH4 flux; CH4 emission averaged 4% of CO2 uptake. End-of-season sedge biomass was also strongly related to CH4 flux, indicating the important role that vascular plants play in regulating CH4 flux. Determination of isotopic signatures in peat pore water CH4 revealed average delta(13)C values of between -50 and -73 parts per thousand and delta D of between -368 and -388 parts per thousand. Sites with large CH4 emission rates also had high CO2 exchange rates and enriched delta(13)C CH4 signatures, suggesting the importance of the acetate fermentation pathway of methanogenesis. Comparison of delta D and delta(13)C signatures in pore water CH4 revealed a slope shallow enough to suggest that oxidation is not an important overall control on CH4 emissions at these sites, though it appeared to be important at one site. Analysis of C- 14 in pore water CH4 showed that most of the CH4 was of recent origin with percent of modern carbon values of between 112 and 128%. The study has shown the importance of vascular plant activities in controlling CH4 emissions from these wetland sites through influences on the availability of fresh plant material for methanogenesis, rhizospheric oxidation, and plant transport of CH4.
erminat2682^2^Pulleman,M^Tietema,A^1999^1^Microbial C and N transformations during drying and rewetting of coniferous forest floor material^130^31^2^275-285^^^^^Feb^^^^^8121
1186^1531^1959^2611^3768^407^427^433^466^sion rates also had high CO2 exchange rates and enriched delta(13)C CH4 signatures, suggesting the importance of the acetate fermentation pathway of methanogenesis. Comparison of delta D and delta(13)C signatures in pore water CH4 revealed a slope shallow enough to suggest that oxidation is not an important overall control on CH4 emissions at these sites, though it appeared to be important at one site. Analysis of C- 14 in pore water CH4 showed that most of the CH4 was of recent origin with percent of modern carbon values of between 112 and 128%. The study has shown the importance of vascular plant activities in controlling CH4 emissions from these wetland sites through influences on the availability of fresh plant material for methanogenesis, rhizospheric oxidation, and plant transport of CH4.
erminatA^8120^Microbial C and N transformation rates in air-dried and subsequently rewetted coniferous forest floor material were examined in a laboratory incubation study. Gross N transformation rates were determined through parallel (NH4+)-N- 15 and (NO3-)-N-15 enrichment experiments. After drying of the litter for 12 d to a water content of 10% of dry weight, CO2 respiration, net N mineralization and nitrification rates were strongly restricted. Microbial biomass C was reduced to 67% of the amount in the continuously moist material. Remoistening of the dry litter to a water content of 340% resulted in a flush in C and net N mineralization within a few hours after rewetting. The increase in net N mineralization could be attributed to a larger increase in gross N mineralization relative to the increase in gross N immobilization. Gross N immobilization had increased to the same rate as gross N mineralization after 26 h, and a small secondary peak in respiration and microbial C was observed 48 h after rewetting. It was concluded that both biomass-derived substrate with a low C-to-N ratio and 'nonbiomass'-derived substrate with a high C- to-N ratio have been released, and metabolized, as a result of the drying-rewetting treatment. Despite the very extreme drying treatment, the mineralization flush after rewetting could not compensate for the large reduction in CO2 and mineral N production during dry conditions due to its short duration. Since there was no increase in nitrification rate after drying and rewetting, the NO3- concentration at the end of the incubation was strongly reduced due to the extremely slow net nitrification rates during desiccation. (C) 1998 Elsevier Science Ltd. All rights reserved.





2684^5^Flagella,Z^Campanile,R G^Stoppelli,M C^De Caro,A^Di Fonzo,N^1998^1^Drought tolerance of photosynthetic electron transport under CO2-enriched and normal air in cereal species^37^104^4^753-759^^^^^Dec^^^^^8125
1092^1240^188^2058^3298^3769^3770^416^493^713^and microbial C was observed 48 h after rewetting. It A^8124^The quantum yield of photosynthetic electron transport (Phi PSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought- tolerant genotypes, three cereal species were studied; Phi PSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal Phi PSII and both the transient and steady-state actual Phi PSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O-2, 0.035% CO2 in N-2) to monitor the whole photosynthetic process under physiological conditions, and CO2 enriched-low O-2 air (1% O-2, 5% CO2 in N- 2) to monitor Phi PSII reduction under stress mainly related to Calvin cycle activity. When Phi PSII related to both assimilatory and non-assimilatory metabolism was evaluated, the cultivar differences observed under normal air were more representative of the agronomic performance upon drought stress than under high CO2-low O-2 air. Maximal Phi PSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The Phi PSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chi fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for.

2685^3^Mavrogianopoulos,G N^Spanakis,J^Tsikalas,P^1999^1^Effect of carbon dioxide enrichment and salinity on photosynthesis and yield in melon^165^79^1-2^51-63^^^^^1 Feb^^^^^8127
256^349^3771^3772^3773^3774^3775^3776^3777^417^ntative of the agronomic performance upon drought stress than under high CO2-low O-2 air. Maximal Phi PSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The Phi PSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chi fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological A^8126^Melon (Cucumis melo L. Cv Parnon) grown in rockwool culture in the greenhouse was CO2 enriched, for 5 h every morning, at 400, 800 and 1200 mu mol mol(-1) and trickle-irrigated with nutrient solutions amended with 0, 25 and 50 mM NaCl. High CO2 level increased fruit yield, the increase being greater in unsalinated plants than in salinated. With total shoot fresh weight, the increase was greater in salinated plants. CO2 enrichment also increased leaf growth and the chlorophyll content of the measured leaves. Addition of NaCl in the nutrient solution caused significant reduction in total yield, the reduction being greater at higher concentrations of CO2, At 25 mM NaCl, the decrease in yield resulted mainly from the smaller fruit size, but at 50 mM yield reduction was due both to smaller fruit size and to fewer fruits per plant. Addition of NaCl caused significant reduction in total shoot fresh weight in all cases, the reduction being greater at the lower level of CO2. Salinity also, significantly reduced leaf surface irrespective of CO2 level. Chlorophyll content was reduced by NaCl mainly at the level of 50 mM NaCl. A stronger correlation was found between salinity and shoot fresh weight, plant height and leaf surface area, than salinity and yield and other characteristics. Measurements of gas exchange showed that, for the above mentioned CO2 and NaCl concentrations, net assimilation was affected by CO2 to a greater degree than by salinity. Stomatal conductance was most affected by salinity at a concentration of 50 mM NaCl. (C) 1999 Elsevier Science B.V. All rights reserved.

2686^4^Wang,X F^Li,S Y^Bai,K Z^Kuang,T Y^1998^1^Influence of doubled CO2 on plant growth and soil microbial biomass C and N^384^40^12^1169-1172^^^^^^^^^^8129
1959^374^3778^57^879^ld reduction was due both to smaller fruit size and to fewer fruits per plant. Addition of NaCl caused significant reduction in total shoot fresh weight in all cases, the reduction being greater at the lower level of CO2. Salinity also, significantly reduceA^8128^Salix babylonica L. Triticum aestivum L. Chenopodium album L. and Amaranthus cruentus L. were grown in the N-deficient soil in open-top chambers blown with ambient or doubled ambient CO2 air, and their growth was measured. Soil samples were collected to assess the influence of doubled CO2 on the soil microbial biomass C (C-mic) and N (N-mic). Results showed that the biomass of shoot and root was increased by doubled CO2 in the four species of plants. Doubled CO2 increased C-mic in S. babylonica and decreased C-mic in T. aestivum and C. album. On the other hand, N-mic in three species except T. aestivum was stimulated by doubled CO2. Doubled CO2 had no significant effect on C-mic in A. cruentus and N-mic in T. aestivum. However, the ratios of C-mic- to -N-mic of all four species were consistently declined under doubled CO2 treatment. It implies that CO2 enrichment may have positive influence on the quality of organic matter of N-low soil in global change.
el of CO2. Salinity also, significantly reduce2687^9^Huxman,T E^Hamerlynck,E P^Moore,B D^Smith,S D^Jordan,D N^Zitzer,S F^Nowak,R S^Coleman,J S^Seemann,J R^1998^1^Photosynthetic down-regulation in Larrea tridentata exposed to elevated atmospheric CO2: interaction with drought under glasshouse and field (FACE) exposure^9^21^11^1153-1161^^^^^Nov^^^^^8131
130^312^356^360^374^384^549^552^672^92^c). Results showed that the biomass of shoot and root was increased by doubled CO2 in the four species of plants. Doubled CO2 increased C-mic in S. babylonica and decreased C-mic in T. aestivum and C. album. On the other hand, N-mic in three species except T. aestivum was stimulated by doubled CO2. Doubled CO2 had no significant effect on C-mic in A. cruentus and N-mic in T. aestivum. However, the ratios of C-mic- to -N-mic of all four species were consistently declined under doubled CO2 treatment. It implies that CO2 enrichment may have positive influence on the quality of organic matter of N-low soil in global change.
el of CO2. Salinity also, significantly reduceA^8130^The photosynthetic response of Larrea tridentata Cav,, an evergreen Mojave Desert shrub, to elevated atmospheric CO2 and drought was examined to assist in the understanding of how plants from water-limited ecosystems will respond to rising CO2, We hypothesized that photosynthetic down-regulation would disappear during periods of water Limitation, and would, therefore, likely be a seasonally transient event. To test this we measured photosynthetic, water relations and fluorescence responses during periods of increased and decreased mater availability in two different treatment implementations: (1) from seedlings exposed to 360, 550, and 700 mu mol mol(-1) CO2 in a glasshouse; and (2) from intact adults exposed to 360 and 550 mu mol mol(-1) CO2 at the Nevada Desert FACE (Free Air CO2 Enrichment) Facility. FACE and glasshouse wed-watered Larrea significantly down-regulated photosynthesis at elevated CO2, reducing maximum photosynthetic rate (A(max)), carboxylation efficiency (CE), and Rubisco catalytic sites, whereas droughted Larrea showed a differing response depending on treatment technique. A(max) and CE were lower in droughted Larrea compared with well-watered plants, and CO2 had no effect on these reduced photosynthetic parameters. However, Rubisco catalytic sites decreased in droughted Larrea at elevated CO2. Operating C-i increased at elevated CO2 in droughted plants, resulting in greater photosynthetic rates at elevated CO2 as compared with ambient CO2. In well-watered plants, the changes in operating C-i, CE andA(max) resulted in similar photosynthetic rates across CO2 treatments. Our results suggest that drought can diminish photosynthetic down-regulation to elevated CO2 in Larrea, resulting in seasonally transient patterns of enhanced carbon gain. These results suggest that water status may ultimately control the photosynthetic response of desert systems to rising CO2.
ynthesis at elevated CO2, reducing maximum photosynthetic rate (A(max)), carboxylation efficiency (CE), and Rubisco catalytic s2688^6^Reicosky,D C^Reeves,D W^Prior,S A^Runion,G B^Rogers,H H^Raper,R L^1999^1^Effects of residue management and controlled traffic on carbon dioxide and water loss^370^52^3-4^153-165^^^^^Oct^^^^^8133
1140^23^3779^57^738^tic parameters. However, Rubisco catalytic sites decreased in droughted Larrea at elevated CO2. Operating C-i increased at elevated CO2 in droughted plants, resulting in greater photosynthetic rates at elevated CO2 as compared with ambient CO2. In well-watered plants, the changes in operating C-i, CE andA(max) resulted in similar photosynthetic rates across CO2 treatments. Our results suggest that drought can diminish photosynthetic down-regulation to elevated CO2 in Larrea, resulting in seasonally transient patterns of enhanced carbon gain. These results suggest that water status may ultimately control the photosynthetic response of desert systems to rising CO2.
ynthesis at elevated CO2, reducing maximum photosynthetic rate (A(max)), carboxylation efficiency (CE), and Rubisco catalytic sA^8132^Management of crop residues and soil organic matter is of primary importance in maintaining soil fertility and productivity and in minimizing agricultural impact on the environment. Our objective was to determine the effects of traffic and tillage on short-term carbon dioxide (CO2) and water (H2O) fluxes from a representative soil in the southeastern Coastal Plain (USA). The study was conducted on a Norfolk loamy sand (FAO classification, Luxic Ferralsols; USDA classification, fine-loamy siliceous, thermic Typic Kandiudults) cropped to a corn (Zea mays L.)- soybean (Glycine maw (L.) Merr) rotation with a crimson clover (Trifolium incarnatum L.) winter cover crop for eight years. Experimental variables were with and without traffic under conventional tillage (CT) (disk harrow twice, chisel plow, field cultivator) and no tillage (NT) arranged in a split-plot design with four replicates. A wide-frame tractive vehicle enabled tillage without wheel traffic. Short-term CO2 and H2O fluxes were measured with a large portable chamber. Gas exchange measurements were made on both CT and NT at various times associated with tillage and irrigation events. Tillage-induced COP and H2O fluxes were larger than corresponding fluxes from untilled soil. Irrigation caused the CO2 fluxes to increase rapidly from both tillage systems, suggesting that soil gas fluxes were initially limited by lack of water. Tillage-induced CO2 and H2O fluxes were consistently higher than under NT. Cumulative CO2 flux from CT at the end of 80 h was nearly three times larger than from NT while the corresponding H2O loss was 1.6 times larger. Traffic had no significant effects on the magnitude of CO:! fluxes, possibly reflecting this soil's natural tendency to reconsolidate. The immediate impact of intensive surface tillage of sandy soils on gaseous carbon loss was larger than traffic effects and suggests a need to develop new management practices for enhanced soil carbon and water management for these sensitive soils. (C) 1999 Elsevier Science B.V. All rights reserved.

2689^3^Ver,L M B^Mackenzie,F T^Lerman,A^1999^1^Biogeochemical responses of the carbon cycle to natural and human perturbations: Past, present, and future^398^299^7-9^762-801^^^^^Sep-Nov^^^^^8135
1617^1637^1660^1919^344^3780^3781^625^715^931^xes to increase rapidly from both tillage systems, suggesting that soil gas fluxes were initially limited by lack of water. Tillage-induced CO2 and H2O fluxes were consistently higher than under NT. Cumulative CO2 flux from CT at the end of 80 h was nearly three times larger than from NT while the corresponding H2O loss was 1.6 times larger. Traffic had no significant effects on the magnitude of CO:! fluxes, possibly reflecting this soil's natural tendency to reconsolidate. The immediate impact of intensive surface tillage of sandy soils on gaseous carbon loss was larger than traffic effects and suggests a need to develop new management practices for enhanced soil carbon and water management for these sensitive soils. (C) 1999 Elsevier Science B.VA^8134^In the past three centuries, human perturbations of the environment have affected the biogeochemical behavior df the global carbon cycle and that of the other three nutrient elements closely coupled to carbon: nitrogen, phosphorus, and sulfur. The partitioning of anthropogenic CO2 among its various sinks in the past, for the present, and for projections into the near future is controlled by the interactions of these four elemental cycles within the major environmental domains of the land, atmosphere, coastal oceanic zone, and open ocean. We analyze the past, present, and future behavior of the global carbon cycle using the Terrestrial-Ocean-aTmosphere Ecosystem Model (TOTEM), a unique process-based model of the four global coupled biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur. We find that during the past 300 yrs, anthropogenic CO2 was mainly stored in the atmosphere and in the open ocean. Human activities on land caused an enhanced loss of mass from the terrestrial organic matter reservoirs (phytomass and humus) mainly through deforestation and consequently increased humus remineralization, erosion, and transport to the coastal margins by rivers and runoff. Photosynthetic uptake by the terrestrial phytomass was enhanced owing to fertilization by increasing atmospheric CO2 concentrations and supported by nutrients remineralized from organic matter. TOTEM results indicate that through most of the past 300 yrs, the loss of C from deforestation and other land-use activities was greater than the gain from the enhanced photosynthetic uptake. During the decade of the 1980s, the terrestrial organic reservoirs were in rough carbon balance. Organic and carbonate carbon accumulating in coastal marine sediments is a small but significant sink for anthropogenic CO2. Increasing inputs of terrestrial organic matter and its subsequent oxidation in the coastal margin (increasing heterotrophy) were significant sources of CO2 in coastal waters in the 20th century. However, the coastal ocean did not evolve into a greater net source of CO2 to the atmosphere during this period because of the opposing pressure from rising atmospheric CO2. Since pre-industrial time (since 1700), the net nux of CO2 from the coastal waters has decreased by 40 percent, from 0.20 Gt C/yr to 0.12 Gt C/yr. TOTEM analyses of atmospheric CO2 concentrations for the 21st century were based on the fossil-fuel emission projections of IPCC ("business as usual" scenario) and of the more restrictive UN 1997 Kyoto Protocol. By the mid-21st century, the projected atmospheric CO2 concentrations range from about 550 ppmv (TOTEM,based on IPCC projected emissions) to 510 ppmv (IPCC projection) and to 460 ppmv (TOTEM, based on the Kyoto Protocol reduced emissions). The difference of about 40 ppmv between the IPCC and TOTEM estimates by the year 2050 reflects the different mechanisms within the C-N-P-S cycles on land that are built into our model. The effects of the reduced emissions prescribed by the Kyoto Protocol begin to show in the atmospheric CO2 concentrations by the mid-21st century, when our model projects a rise to 460 (year 2050) and 490 ppmv (2075), relative to about 360 ppmv in 1995. However, these projected increases assume no major changes in the present biogeochemical feedback mechanisms within the system of the coupled C-N-P-S cycles, no global changes in the kind and distribution of ecosystems in response to the rising CO2 and possibly temperature, and no changes in the mechanisms of CO2 exchange between the atmosphere and the ocean, such as could be induced by changes in the intensity of oceanic thermohaline circulation.

2690^2^Krishnan,P^Ramakrishnayya,G^1999^1^Survival of rice during complete submergence: effect of potassium bicarbonate application^92^26^8^793-800^^^^^^^^^^8137
174^1989^3782^92^and TOTEM estimates by the year 2050 reflects the different mechanisms within the C-N-P-S cycles on land that are built into our model. The effects of the reduced emissions prescribed by the Kyoto Protocol begin to show in the atmospheric A^8136^The effect of potassium bicarbonate application to floodwater on the survival and growth of submergence-tolerant (FR13A) and -intolerant (IR42) rice cultivars during complete submergence was investigated. Potassium bicarbonate, applied at different rates to enhance floodwater carbon dioxide concentrations, increased the floodwater oxygen concentration. The treatment that had CuSO4, added alone to reduce algal growth showed the lowest O-2 concentration at the time of submergence and after 10 d of submergence. Potassium bicarbonate at higher rates tended to maintain the floodwater pH near neutrality while copper sulfate affected pH increase during a 10-day period of complete submergence. Potassium bicarbonate addition led to 100% survival of tolerant FR13A. Potassium bicarbonate, even at 0.01 mol m(-3) enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0 mol m(-3), the survival was above 85%. Dry weights of submerged plants showed increases in both rice cultivars in floodwater treated with potassium bicarbonate. The dry weight and leaf chlorophyll concentration of both cultivars increased with increasing rates of potassium bicarbonate. Algal chlorophyll concentration of floodwater treated with potassium bicarbonate was comparable to that of the control without copper sulfate. The findings suggest a possibility of environmental manipulation of floodwater by potassium bicarbonate application to enhance the survival and growth of rice cultivars during complete submergence.

2691^8^Wardle,D A^Bonner,K I^Barker,G M^Yeates,G W^Nicholson,K S^Bardgett,R D^Watson,R N^Ghani,A^1999^1^Plant removals in perennial grassland: Vegetation dynamics, decomposers, soil biodiversity, and ecosystem properties^75^69^4^535-568^^^^^Nov^^^^^8139
3783^3784^3785^3786^3787^3788^3789^3790^3791^535^at 0.01 mol m(-3) enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0 mol m(-3), the survival was above 85%. Dry weights of submerged plants showed increases in both rice cultivars in floodwater treatedA^8138^The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or "functional groups" of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C-3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C-4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C-4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C-4 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe- feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C-4 grasses enhanced diversity; there were negative correlations between plant and arthropod diversity, presumably because of negative influences of C-4 species in the most diverse treatments. There was evidence of lag relationships between diversity of plants and that of the three decomposer groups, indicating multitrophic effects of altering plant diversity. Relatively small effects of plant removal on the decomposer food web were also apparent in soil processes regulated by this food web. Decomposition rates of substrates added to soils showed no relationship with treatment, and rates of CO2 evolution from the soil were only adversely affected when all plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusion of plant species from the species pool can have important consequences for overall vegetation composition in addition to the direct effects of vegetation removal, and various potential effects on both the above- and belowground subsystems. The nature of many of these effects is driven by which plant species are lost from the system, which depends on the various attributes or traits of these species.

2692^3^Velikova,V^Tsonev,T^Yordanov,I^1999^1^Light. and CO2 responses of photosynthesis and chlorophyll fluorescence characteristics in bean giants after simulated acid rain^37^107^1^77-83^^^^^Sep^^^^^8141
130^2171^348^384^386^388^447^635^637^92^plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusionA^8140^The effects of simulated acid rain on some chlorophyll fluorescence characteristics and photosynthetic gas exchange at different light intensities and CO2 concentrations of bean plants were investigated. Measurements were carried out 3, 5 and 24 h after spraying. The results showed that a single acid rain (pH 1.8) treatment of bean plants reduced gas exchange, the maximal carboxylating efficiency and photochemical quenching, This treatment led also to increased CO2 compensation point and non-photochemical quenching and changed the shape of CO2 and light curves of photosynthesis, Both stomatal and non-stomatal factors contributed to the decreased photosynthetic rate, but their proportion changed with time of recovery of the photosynthetic apparatus. Three hours after the treatment, the stomatal factors predominated in photosynthesis reduction, while during the next experimental period (5-24 h), mainly non-stomatal factors determined the decreased photosynthetic rate, It is suggested that the effects observed in consequence of acid rain treatment could be due to an increased intracellular accumulation of H+ and harmful ions contained in the cocktail, This probably led to impaired membrane permeability, enhancement of stroma acidity, uncoupled electron transport and insufficient accumulation of ATP and NADPH, which affected carbon metabolism.

2693^1^Erickson,D J^1999^1^Nitrogen deposition, terrestrial carbon uptake and changes in the seasonal cycle of atmospheric CO2^65^26^21^3313-3316^^^^^1 Nov^^^^^8143
2137^314^362^529^92^hanged the shape of CO2 and light curves of photosynthesis, Both stomatal and non-stomatal factors contributed to the decreased photosynthetic rate, but their proportion changed with time of recovery of the photosynthetic apparatus. Three hours after the treatment, the stomatal factors predominated in photosynthesis reduction, while during the next experimental period (5-24 h), mainly non-stomatal factors determined the decreased photosynthetic rate, It is suggested that the effects obA^8142^Observational evidence indicates an increasing trend in the amplitude of the seasonal cycle of atmospheric CO2 over the last several decades. Here, the influence of nitrogen deposition on the seasonal cycle of atmospheric CO2 is investigated using a global carbon cycle model embedded in a 3- D general circulation model. We employ a recently published estimate of the enhancement of carbon dioxide uptake induced by the atmospheric deposition of NOy and NHx. We partition the carbon sink related to nitrogen deposition over the seasonal cycle of CO2 uptake. The modeled increase in the amplitude of the seasonal cycle of CO2 in the Northern Hemisphere related to the simulated nitrogen deposition alone is 25%-50% of observed. At Mauna Loa the increased amplitude in the CO2 seasonal cycle due to nitrogen deposition is 50-90% of that observed. The subtle interaction between 3-D atmospheric transport, atmospheric nitrogen deposition, and seasonal CO2 uptake results in significant changes in the amplitude of the seasonal cycle of atmospheric CO2. The magnitude of these nitrogen deposition-induced changes in the atmospheric behavior of CO2 is comparable to other processes that are thought to influence global carbon cycle dynamics.

2694^5^Flexas,J^Badger,M^Chow,W S^Medrano,H^Osmond,C B^1999^1^Analysis of the relative increase in photosynthetic O-2 uptake when photosynthesis in grapevine leaves is inhibited following low night temperatures and/or water stress^8^121^2^675-684^^^^^Oct^^^^^8145
1092^1148^1168^188^3792^417^493^603^635^713^the seasonal cycle of CO2 uptake. The modeled increase in the amplitude of the seasonal cycle of CO2 in the Northern Hemisphere related to the simulated nitrogen deposition alone is 25%-50% of observed. At Mauna Loa the increased amplitude in the CO2 seasonal cycle due to nitrogen deposition is 50-90% of that observed. The subtle interaction between 3-D atmospheric transport, atmospheric nitrogen deposition, and seasonal CO2 uptake results in significant changes in the amplitude of the A^8144^We found similarities between the effects of low night temperatures (5 degrees C-10 degrees C) and slowly imposed water stress on photosynthesis in grapevine (Vitis vinifera L.) leaves. Exposure of plants growing outdoors to successive chilling nights caused light- and CO2 saturated photosynthetic O-2 evolution to decline to zero within 5 d. Plants recovered after four warm nights. These photosynthetic responses were confirmed in potted plants, even when roots were heated. The inhibitory effects of chilling were greater after a period of illumination, probably because transpiration induced higher water deficit. Stomatal closure only accounted for part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O-2 evolution, even at high external CO2 concentrations. Oxygen isotope exchange revealed that this imbalance was due to increased O-2 uptake, which probably has two components: photorespiration and the Mehler reaction. Chilling- and drought-induced water stress enhanced both O-2 uptake processes, and both processes maintained relatively high rates of electron flow as CO2 exchange approached zero in stressed leaves. Presumably, high electron transport associated with O-2 uptake processes also maintained a high Delta pH, thus affording photoprotection.

2695^2^Perumal,J V^Maun,M A^1999^1^The role of mycorrhizal fungi in growth enhancement of dune plants following burial in sand^43^13^4^560-566^^^^^Aug^^^^^8147
243^2999^3793^3794^407^984^part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O-2 evolution, even at high external CO2 concentrations. Oxygen isotope exchange reveA^8146^1, Burial in sand of Agropyron psammophilum and Panicum virgatum plants had a stimulating effect on carbon dioxide exchange rate, leaf area and biomass, irrespective of whether sand used for burial did or did not contain mycorrhizal fungi. 2, Plants of both A. psammophilum and P. virgatum species grown in mycorrhiza-containing sand and then buried with mycorrhiza- containing sand had the highest CO2 exchange rate, leaf area and biomass. 3, The growth stimulation following a burial episode is probably a composite response of several factors. The major contribution of mycorrhizal fungi will possibly be the exploitation of resources in the burial deposit.

2696^1^McMaster,H J^1999^1^The potential impact of global warming on hail losses to winter cereal crops in New South Wales^50^43^2^455-476^^^^^Oct^^^^^8149
130^137^1587^314^3795^909^c response to both stresses was an increase in the ratio of electron transport to net O-2 evolution, even at high external CO2 concentrations. Oxygen isotope exchange reveA^8148^This study was undertaken to determine the impact of potential global warming on the magnitude of hail losses to winter cereal crops within two areas situated on the western slopes of New South Wales, Australia. A model relating historical crop hail losses to climatic variables was developed for each area. These models included seasonal measures of vertical instability, low- level moisture and the height of the freezing level. In both areas, windshear was not found to be an important factor influencing seasonal crop hail losses. The two crop hail loss models were then used in conjunction with upper-air climatic data from three single mixed-layer global climate models (GCMs). Each GCM was run for 1 x CO2 conditions and for 2 x CO2 conditions. The enhanced greenhouse effect on climatic variables was taken to be the difference between their values for these two runs. Changes to climatic variables were then translated directly into changes in the percentage value of the winter cereal crop lost due to hail. In both areas, the three GCMs agreed concerning the direction of change in each of the variables used in the crop hail loss model. GCM simulations of the greenhouse effect resulted in a decline in winter cereal crop hail losses, with the exception of one GCM simulation at one location where losses increased slightly. None of the changes due to the enhanced greenhouse effect, however, were significant owing to a large observed seasonal variability of crop hail losses. Also, the simulated seasonal variability of crop hail losses did not change significantly due to the enhanced greenhouse effect. These results depended on two important assumptions. Firstly, it was assumed that the dominant relationships between climatic variables and crop hail losses in the past would remain the same in a future climate. Secondly, it was assumed that the single mixed-layer GCMs used in the study were correctly predicting climate change under enhanced greenhouse conditions.
age value of the winter cereal crop lost due to hail2697^1^Trenberth,K E^1999^1^Conceptual framework for changes of extremes of the hydrological cycle with climate change^50^42^1^327-339^^^^^May^^^^^8151
1203^1356^174^314^3665^3796^413^633^668^888^n winter cereal crop hail losses, with the exception of one GCM simulation at one location where losses increased slightly. None of the changes due to the enhanced greenhouse effect, however, were significant owing to a large observed seasonal variability of crop hail losses. Also, the simulated seasonal variability of crop hail losses did not change significantly due to the enhanced greenhouse effect. These results depended on two important assumptions. Firstly, it was assumed that the dominant relationships between climatic variables and crop hail losses in the past would remain the same in a future climate. Secondly, it was assumed that the single mixed-layer GCMs used in the study were correctly predicting climate change under enhanced greenhouse conditions.
age value of the winter cereal crop lost due to hailA^8150^A physically based conceptual framework is put forward that explains why an increase in heavy precipitation events should be a primary manifestation of the climate change that accompanies increases in greenhouse gases in the atmosphere. Increased concentrations of greenhouse gases in the atmosphere increase downwelling infrared radiation, and this global heating at the surface not only acts to increase temperatures but also increases evaporation which enhances the atmospheric moisture content. Consequently all weather systems, ranging from individual clouds and thunderstorms to extratropical cyclones, which feed on the available moisture through storm- scale moisture convergence, are likely to produce correspondingly enhanced precipitation rates. Increases in heavy rainfall at the expense of more moderate rainfall are the consequence along with increased runoff and risk of flooding. However, because of constraints in the surface energy budget, there are also implications for the frequency and/or efficiency of precipitation. It follows that increased attention should be given to trends in atmospheric moisture content, and datasets on hourly precipitation rates and frequency need to be developed and analyzed as well as total accumulation.





2699^4^Aggangan,R T^O'Connell,A M^McGrath,J F^Dell,B^1999^1^The effects of Eucalyptus globulus Labill. leaf letter on C and N mineralization in soils from pasture and native forest^130^31^11^1481-1487^^^^^Oct^^^^^8155
1031^19^1959^2796^3019^310^3246^3797^3798^56^equently all weather systems, ranging from individual clouds and thunderstorms to extratropical cyclones, which feed on the available moisture through storm- scale moisture convergence, are likely to produce correspondingly enhanced precipitation rates. Increases in heavy rainfall at the expense of more moderate rainfall are the consequence along with increased runoff and risk of flooding. However, because of constraints in the surface energy budget, there are also implications for the frequency and/or efficA^8154^The effects of addition of Eucalyptus globulus leaf litter on carbon and nitrogen mineralization in soils from a pasture and a native forest were evaluated using a long-term laboratory aerobic incubation assay (29 weeks at 20 degrees C) in leaching microlysimeters, The amount of added leaf litter significantly influenced microbial respiration, microbial biomass and N turnover in both the native forest and pasture soils. Cumulative CO2-C respired increased with increasing rate of leaf litter addition when leaf litter was mixed through the soil or placed on the soil surface. These increases were associated with increases in microbial biomass C content. Cumulative net N mineralization declined in ail treatments when litter was added and was lowest when leaf litter was mixed with soil. When leaf litter was added in increasing amounts to the soil surface, there was a concomitant increase in microbial biomass N content (r(2) = 0.79, n = 8), indicating that the reduction in net N mineralization was primarily due to immobilization of N in microbial tissues. In contrast, when litter was mixed with soil in increasing amounts, there was a decrease in microbial biomass N in forest soil and an increase in pasture soil. Consequently, changes in the rate of net N mineralization were not well related to changes in microbial biomass N content. It is suggested that this may be due to the greater activity and more rapid turnover of microorganisms where litter was incorporated resulting in more of the immobilized N being partitioned into metabolic products or dead microbial cells. Incorporation of litter may also have enhanced loss N through denitrification, (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

2700^1^Mortensen,L M^1999^1^Foliar injuries caused by ozone in Betula pubescens Ehrh. and Phleum pratense L. as influenced by climatic conditions before and during O-3 exposure^200^49^1^44-49^^^^^Mar^^^^^8157
130^243^310^3146^361^430^674^92^923^ing that the reduction in net N mineralization was primarilyA^8156^Seedlings of Betula pubescens Ehrh. (mountain birch) and Phleum pratense L. (timothy) were grown for 42 days under full light or 50% shade in the field at 12 degrees C, and at comparable photosynthetic active radiation (PAR) levels in a greenhouse at 18 degrees C. Plants from the four pretreatments were exposed to 78 nmol mol(-1) (ppb) O-3 (8 h day(-1)) under two temperatures (15 and 25 degrees C), two relative air humidities (50 and 80% RH) or two CO2 concentrations (400 and 750 mu mol mol(-1)) during 7 days. The accumulated O-3 dose over 40 nmol mol(-1) O-3 (AOT40) was 2.6 mu mol mol(-1)-hours (ppm-h). Decreasing the temperature during exposure significantly increased the amount of injury induced by O-3 in leaves of birch (yellow mottling/bronzing) as well as timothy (chlorosis/necrosis). Increasing the air humidity or decreasing the CO2 concentration strongly enhanced the injuries caused by O-3 in timothy, but not in birch. In general, both birch and timothy plants grown in the greenhouse and in the field had the same O-3 sensitivity. However, decreasing the PAR level during the pretreatment enhanced leaf injury in birch but not in timothy. At the most sensitive exposure climate, 15 degrees C/80% RH, leaf injury developed at an AOT40 of 0.7-0.9 ppm-h in both species.

2701^3^Vervuren,P J A^Beurskens,S M J H^Blom,C W P M^1999^1^Light acclimation, CO2 response and long-term capacity of underwater photosynthesis in three terrestrial plant species^9^22^8^959-968^^^^^Aug^^^^^8159
1020^1163^1189^1619^1989^2245^639^851^92^cumulated O-3 dose over 40 nmol mol(-1) O-3 (AOT40) was 2.6 mu mol mol(-1)-hours (ppm-h). Decreasing the temperature during exposure significantly increased the amount of injury induced by O-3 in leaves of birch (yellow mottling/bronzing) as well as timothy (chlorosis/necrosis). Increasing the air humidity or decreasing the CO2 concentration strongly enhanced the injuries caused by O-3 in timothy, but not in birch. In general, both birch and timothy plants grown in the greenhouse and in thA^8158^To characterize underwater photosynthetic performance in some terrestrial plants, we determined (i) underwater light acclimation (ii) underwater photosynthetic response to dissolved CO2, and (iii) underwater photosynthetic capacity during prolonged submergence in three species that differ in submergence tolerance: Phalaris arundinacea, Rumex crispus (both submergence-tolerant) and Arrhenatherum elatius (submergence-intolerant). None of the species had adjusted to low irradiance after 1 week of submergence. Under non-submerged (control) conditions, only R. crispus displayed shade acclimation, Submergence increased the apparent quantum yield in this species, presumably because of the enhanced CO2 affinity of the elongated leaves, In control plants of the grass species II arundinacea and A. elatius, CO2 affinities were higher than for R, crispus. The underwater photosynthetic capacity of R. crispus increased during 1 month of submergence. In P. arundinacea photosynthesis remained constant during 1 month of submergence at normal irradiance; at low irradiance a reduction in photosynthetic capacity was observed after 2 weeks, although there was no tissue degeneration, In contrast, underwater photosynthesis of the submergence-intolerant species A, elatius collapsed rapidly under both irradiances, and this was accompanied by leaf decay, To describe photosynthesis versus irradiance curves, four models were evaluated, The hyperbolic tangent produced the best goodness-of-fit, whereas the rectangular hyperbola (Michaelis-Menten model) gave relatively poor results.

2702^3^Alvarez,R^Alconada,M^Lavado,R^1999^1^Sewage sludge effects on carbon dioxide-carbon production from a desurfaced soil^222^30^13-14^1861-1866^^^^^^^^^^8161
2923^3304^3799^3800^3801^537^720^ts of the grass species II arundinacea and A. elatius, CO2 affinities were higher than for R, crispus. The underwater photosynthetic capacity of R. crispus increased during 1 month of submergence. In P. arundinacea photosynthesis remained constant during 1 month A^8160^Desurfaced soils are found near cities in the Pampean Region of Argentina because A horizons were used for brick production. These soils are not suitable for agriculture. Application of sewage sludge is a tool for improving soil productivity, but its effects on the environment are not thoroughly understood. Production of carbon dioxide (CO2)-carbon (C) in the field from a desurfaced soil in which 25 Mg dry matter ha(-1) of sewage sludge were applied the first year and 10 Mg dry matter ha(-1), the second year was evaluated during a corn (Zea mays L.) growing cycle. Microbial biomass and metabolic activity were also measured. Sludge applications produced an increase of the CO2-C efflux in the field of 30-50% during summer. Microbial biomass was not affected by sludge some months after the application, but metabolic activity and organic matter mineralization were enhanced. The increase of the CO2-C emission from the soil represented 21% of the sludge C applied the year of the experiment and 15% of the C applied the year before. Consequently, an important quantity of the sludge C was retained in the soil.

2703^4^Lee,X H^Fuentes,J D^Staebler,R M^Neumann,H H^1999^1^Long-term observation of the atmospheric exchange of CO2 with a temperate deciduous forest in southern Ontario, Canada^278^104^D13^15975-15984^^^^^20 Jul^^^^^8163
1180^1484^227^23^3802^393^431^633^673^729^field from a desurfaced soil in which 25 Mg dry matter ha(-1) of sewage sludge were applied the first year and 10 Mg dry matter ha(-1), the second year was evaluated during a corn (Zea mays L.) growing cycle. Microbial biomass and metabolic activity were also measured. Sludge applications produced an increase of the CO2-C efflux in the field of 30-50% during summer. Microbial biomass was not affected by sludge some months after the application, but metabolic activity and organic matter mineralization were enhanced. The increase of the CO2-C emission from the soil represented 21% of the sludge C applied the year of the experiment and 15% of the C A^8162^This paper reports the results of the analysis of eddy covariance CO2 data obtained at a successional forest of maple and aspen at Camp Borden in southern Ontario, Canada, between July 1995 and December 1997. Main findings are (1) The Michaelis-Menton model explains >50-65% of the observed variance of the daytime net ecosystem carbon exchange (NEE) during the growing season; leaf wetness appears to be an important variable contributing to the remaining variance. (2) The whole-ecosystem respiration rate as a function of the 5-cm soil temperature shows a seasonal "hysteresis" (higher rate in the later part of the year), suggesting a nonnegligible contribution by deep soil/roots and the influence of litter age. (3) There is evidence of photosynthetic activities immediately after the spring snowmelt/soil warming, but the. daily NEE did not switch sign till about 40 days later; our best estimates of the annual net carbon uptake by the ecosystem net ecosystem production (NEP) are -1,0, -1.2, and -2.8 t C ha(-1) yr(-1) for the periods July 19, 1995, to July 18, 1996, January 1 to December 31, 1996, and January 1 to December 31, 1997, respectively, with an uncertainty of +/-0.4 t C ha(-1) yr(-1). (4) The higher NEP value in 1997 than in 1996 was caused by lower growing season soil temperature, cooler spring and fall transitional periods, and higher photon flux in 1997; possible enhancement in canopy photosynthetic capacity may also have played a role. In addition, three main sources of uncertainties, data gap, fetch, and mass flow, are discussed, it is suggested that collective use of the methods available for assessing the whole-ecosystem respiration (friction velocity threshold, mass flow theory, and dark respiration from the forest light response) may increase the confidence level of NEP estimates.

2704^3^Sun,J D^Edwards,G E^Okita,T W^1999^1^Feedback inhibition of photosynthesis in rice measured by O-2 dependent transients^91^59^2-3^187-200^^^^^Mar^^^^^8165
1240^1713^1912^2178^2242^3095^493^635^713^786^C haA^8164^The kinetic properties of photosynthesis (both transient and steady-state) were monitored using three non-invasive techniques to evaluate limitations on triose-phosphate (triose- P) conversion to carbohydrate in rice. These included analyzing the O-2 sensitivity of CO2 fixation and the assimilatory charge (AC) using gas exchange (estimate of the ribulose 1,5- bisphosphate pool) and measuring Photosystem II activity by chlorophyll fluorescence analysis under varying light, temperature and CO2 partial pressures. Photosynthesis was inhibited transiently upon switching from 20 to 2 kPa O-2 (reversed O-2 sensitivity), the degree of which was correlated with a terminal, steady-state suppression of low O-2 enhancement of photosynthesis. Under current ambient levels of CO2 and moderate to high light, the transient pattern was more obvious at 18 degrees C than at 26 degrees C while at 34 degrees C no transient response was observed. The transient inhibition at 18 degrees C ranged from 15% to 31% depending on the pre-measurement temperature. This pattern, symptomatic of feedback, was observed with increasing light and CO2 partial pressures with the degree of feedback decreasing from moderate (18 degrees C) up to high temperature (34 degrees C). Under feedback conditions, the rate of assimilation is shifted from being photorespiration limited to being triose-P utilization limited. Transitory changes in CO2 assimilation rates (A) under low O-2 indicative of feedback coincided with a transitory drop in assimilatory charge (AC) and inhibition of electron transport. In contrast to previous studies with many C-3 species, our studies indicate that rice shows susceptibility to feedback inhibition under moderate temperatures and current atmospheric levels of CO2.

2705^2^Baattrup-Pedersen,A^Madsen,T V^1999^1^Interdependence of CO2 and inorganic nitrogen on crassulacean acid metabolism and efficiency of nitrogen use by Littorella uniflora (L.) Aschers^9^22^5^535-542^^^^^May^^^^^8167
1305^2058^2868^360^3803^3804^92^ing on tA^8166^The hypothesis is tested that crassulacean acid metabolism (CAM) in isoetids is a mechanism which not only conserves inorganic carbon but also plays a role in nitrogen economy of the plants, This hypothesis was tested in an outdoor experiment, where Littorella uniflora (L,) Aschers, were grown at two CO2 and five inorganic nitrogen concentrations in a crossed factorial design. The growth of Littorella responded positively to enhanced nitrogen availability at high but not at low CO2 indicating that growth was limited by nitrogen at high CO2 only. For the nitrogen-limited plants, the capacity for CAM (CAM(cap)) increased with the degree of nitrogen limitation of growth and an inverse coupling between CAM and tissue-N was found. Although this might indicate a role of CAM in economizing on nitrogen in Littorella, the hypothesis was rejected for the following reasons: (1) although CAM(cap) was related to tissue-N no relationship between tissue-N and ambient CAM activity (CAM(ambient)) was found whereas a close relationship would be expected if CAM was regulated by nitrogen availability; (2) the photosynthetic nitrogen use efficiency for high CO2-grown plants declined with increased CAM(ambient) and with CAM(cap); and (3) growth per unit tissue-N per unit time declined with increased CAM(ambient) and CAM(cap).

2706^4^Noctor,G^Arisi,A C M^Jouanin,L^Foyer,C H^1999^1^Photorespiratory glycine enhances glutathione accumulation in both the chloroplastic and cytosolic compartments^78^50^336^1157-1167^^^^^Jul^^^^^8169
1116^1145^1572^2346^2474^3805^3806^3807^3808^3809^ nitrogen-limited plants, the capacity for CAM (CAM(cap)) increased with the degree of nitrogen limitation of growth and an inverse coupling between CAM and tissue-N was found. Although this might indicate a role of CAM in economizing on nitrogen in Littorella, the hypothesis was rejected for the following reasons: (1) although CAM(cap) was related to tissue-N no relationship between tissue-N and ambient CAM activity (CAM(ambient)) was found whereas a cA^8168^Transformed poplars overexpressing gamma-glutamylcysteine synthetase (gamma-ECS) in the chloroplast (Lggs) were used to investigate chloroplastic biosynthesis of glutathione (GSH), In Lggs leaves, GSH contents were! enhanced by up to 3.7-fold. In general, the highest GSH contents were observed in lines with highest gamma-glutamylcysteine (gamma-EC) contents. These lines had relatively low glycine, In darkness, foliar GSH decreased and gamma-EC increased. Illumination of pre-darkened Lggs in air resulted in a 5-fold decrease in the gamma-EC:GSH ratio, This light-induced decrease was largely abolished if leaves were illuminated at high CO2. Con Consequently, the gamma- EC:GSH ratio of illuminated leaves was much higher at high CO2 than in air. At high CO2 total foliar amino acids were higher, but glycine and serine were lower, than in air, These results suggest that photorespiratory glycine is used in chloroplastic GSH synthesis, Despite this, net CO2 fixation was similar in Lggs to untransformed poplars. Pre-illuminated leaf discs from Lggs, and poplars overexpressing gamma-ECS in the cytosol (ggs), were incubated in darkness with a range of metabolites. After 15 h, discs from both types of transformant incubated on water had accumulated high levels of gamma-EC and showed marked increases in the y-EC:GSH ratio. Feeding glycine, serine, glycollate or phosphoserine, attenuated the dark-induced changes in the gamma-EC:GSH ratio, whereas 3-phosphoglycerate (PGA), phosphoenolpyruvate, glycerate, and hydroxypyruvate did not. Glycine produced from glycollate was therefore required for maximal GSH accumulation in both the chloroplastic and cytosolic compartment Production of glycine from PGA failed to meet the demand of increased GSH synthetic capacity.

2707^2^Potter,C S^Klooster,S A^1999^1^Detecting a terrestrial biosphere sink for carbon dioxide: Interannual ecosystem modeling for the mid-1980s^50^42^3^489-503^^^^^Jul^^^^^8171
2589^3810^3811^529^673^887^CO2 fixation was similar in Lggs to untransformed poplarA^8170^There is considerable uncertainty as to whether interannual variability in climate and terrestrial ecosystem production is sufficient to explain observed variation in atmospheric carbon content over the past 20-30 years. In this paper, we investigated the response of net CO2 exchange in terrestrial ecosystems to interannual climate variability (1983 to 1988) using global satellite observations as drivers for the NASA- CASA (Carnegie-Ames-Stanford Approach) simulation model. This computer model of net ecosystem production (NEP) is calibrated for interannual simulations driven by monthly satellite vegetation index data (NDVI) from the NOAA Advanced Very High Resolution Radiometer (AVHRR) at 1 degree spatial resolution. Major results from NASA-CASA simulations suggest that from 1985 to 1988, the northern middle-latitude zone (between 30 and 60 degrees N) was the principal region driving progressive annual increases in global net primary production (NPP; i.e., the terrestrial biosphere sink for carbon). The average annual increase in NPP over this predominantly northern forest zone was on the order of +0.4 Pg (10(15) g) C per year. This increase resulted mainly from notable expansion of the growing season for plant carbon fixation toward the zonal latitude extremes, a pattern uniquely demonstrated in our regional visualization results. A net biosphere source flux of CO2 in 1983-1984, coinciding with an El Nino event, was followed by a major recovery of global NEP in 1985 which lasted through 1987 as a net carbon sink of between 0.4 and 2.6 Pg C per year. Analysis of model controls on NPP and soil heterotrophic CO2 fluxes (R-h) suggests that regional warming in northern forests can enhance ecosystem production significantly. In seasonally dry tropical zones, periodic drought and temperature drying effects may carry over with at least a two-year lag time to adversely impact ecosystem production. These yearly patterns in our model-predicted NEP are consistent in magnitude with the estimated exchange of CO2 by the terrestrial biosphere with the atmosphere, as determined by previous isotopic (delta(13)C) deconvolution analysis. Ecosystem simulation results can help further target locations where net carbon sink fluxes have occurred in the past or may be verified in subsequent field studies.

2708^3^Hager,C^Wurth,G^Kohlmaier,G H^1999^1^Biomass of forest stands under climatic change: a German case study with the Frankfurt biosphere model (FBM)^257^51^2^385-401^^^^^Apr^^^^^8173
1234^174^374^3812^3813^529^58^715^939^carbon sink of between 0.4 and 2.6 Pg C per year. Analysis of model controls on NPP and soil heterotrophic CO2 fluxes (R-h) suggests that regional warming in northern forests can enhance ecosystem production significantly. In seasonally dry tropical zones, periodic drought and temperature drying effects may carry over with at least a two-year lag time to adversely impact ecosystem production. These yearly patterns in our model-predicted NEP are consistent in magnitude with the estimated exchange of CO2 by tA^8172^In this contribution, we perform a case study of the German forests. We couple the Frankfurt biosphere model (FBM) with a model of the age class development (AGEDYN). The coupled model is applied to simulate the temporal development of carbon pools in German forests under the influence of climate change taking into account changes in the age class structure. In the base case, the growth of forest stands is simulated using a temporally averaged climate dataset, being representative for the contemporary climate conditions. To assess the sensitivity of forest growth to changes in environmental conditions, the FBM is run in several scenarios. In these simulations the effects both of climate change and of the direct effect of increased levels of atmospheric CO2 on photosynthesis (CO2 fertilization) on forest growth are assessed. In another simulation run with the FBM both effects - climate change and CO2 fertilization are combined. In simulations under present day's climate conditions a good agreement is gained between simulation results and statistical data of the present standing stock carbon density of Germany's forests. A pure climate change leads to a decrease of the annual increments as well as to the climax standing stocks. The negative effect of climate change alone is overcompensated by enhanced photosynthesis in the simulations with combined climate change and CO2 fertilization. In the transient case, the coupled model is used in two scenarios describing first a continuation of present day's climate conditions and second a transient climate change from present conditions (1990) to 2 x CO2 conditions in 2090. Here, the simulations indicate that changes in the forest's age class structure can have a stronger influence on the future carbon balance of the forests in the considered region than the combined effect of climate change and CO2 fertilization.
th the FBM both effects - climate change and CO2 fertilization are combined. In simulations under present day's climate conditions a good agreement is g2709^5^Christensen,T R^Jonasson,S^Callaghan,T V^Havstrom,M^Livens,F R^1999^1^Carbon cycling and methane exchange in Eurasian tundra ecosystems^221^28^3^239-244^^^^^May^^^^^8175
3590^362^ as well as to the climax standing stocks. The negative effect of climate change alone is overcompensated by enhanced photosynthesis in the simulations with combined climate change and CO2 fertilization. In the transient case, the coupled model is used in two scenarios describing first a continuation of present day's climate conditions and second a transient climate change from present conditions (1990) to 2 x CO2 conditions in 2090. Here, the simulations indicate that changes in the forest's age class structure can have a stronger influence on the future carbon balance of the forests in the considered region than the combined effect of climate change and CO2 fertilization.
th the FBM both effects - climate change and CO2 fertilization are combined. In simulations under present day's climate conditions a good agreement is gA^8174^This paper provides an overview of data and results obtained through a number of studies of actual and potential trace gas exchanges in northern Eurasia, made possible through the Swedish-Russian Tundra Ecology -94 expedition. It was found that: i) long-term accumulation rates of carbon in organic tundra soils, i.e. net uptake of atmospheric CO2, correlated with simple climatic parameters, such as mean July temperature and annual precipitation; ii) the release of carbon through ecosystem respiration is also strongly controlled by climate. Increased temperature and decrease of water-logging enhanced the CO2 flux. However, the release of organic soil carbon as CO2 is also constrained by other factors such as poor decomposability of the stored organic compounds; and iii) methane emissions from typical tundra habitats in northern Eurasia were found to be slightly lower than from seemingly similar habitats in North America. This difference can probably be attributed to lower temperatures along the Russian arctic coast than at North American sites in general.

2710^2^Drake,S R^Yazdaniha,A^1999^1^Short-term controlled atmosphere storage for shelf-life extension of apricots^399^23^1^57-70^^^^^May^^^^^8177
3737^3814^ology -94 expedition. It was found that: i) long-term accumulation rates of carbon in organic tundra soils, i.e. net uptake of atmospheric CO2, correlated with simple climatic parameters, such as mean July temperature and annual precipitation; ii) the release of carbon through ecosystem respiration is also strongly controlled by climate. Increased temperature and decrease of water-logging enhanced the CO2 flux. However, the release of organic soil carbon as CO2 is also constrained by other factors such as poor decomposability of the stored organic compounds; and iii) methane emissions from typical tundra habitats in northern Eurasia were found to be slightly lower than from seemingly similar habitats in North America. This difference can probably be attributed to lower temperatures along the Russian A^8176^Shelf-life of 'Perfection' and 'Rival' apricots can be enhanced with the use of controlled atmosphere (CA) storage. Apricots were harvested at commercial maturity and immediately stored in CA at 1 or 2 % O-2 and 3, 6, 9, 12 or 15 % CO2 for 30, 45 and 60 days. No differences in fruit quality were evident between O-2 atmospheres of 1 and 2 %, except that fruit stored in 1 % O-2 displayed less rot development and higher acid content. Apricots stored in 9 % or less CO2 displayed reduced external and internal color, inadequate finish, increased internal breakdown and more rot development with unacceptable firmness retention for additional handling. Apricots stored in 12 or 15 % CO2 retained firmness and displayed enhanced finish with reduced rots and very little internal breakdown with storage duration of 60 days. Color was much slower to develop in apricots stored in 12 or 15 % CO2 for all storage periods.




th America. This difference can probably be attributed to lower temperatures along the Russian 2712^2^Reddy,S R C^Price,C^1999^1^Carbon sequestration and conservation of tropical forests under uncertainty^400^50^1^17-35^^^^^Jan^^^^^8181
2171^227^2406^2663^2773^3815^454^738^ately stored in CA at 1 or 2 % O-2 and 3, 6, 9, 12 or 15 % CO2 for 30, 45 and 60 days. No differences in fruit quality were evident between O-2 atmospheres of 1 and 2 %, except that fruit stored in 1 % O-2 displayed less rot development and higher acid content. Apricots stored in 9 % or less CO2 displayed reduced external and internal color, inadequate finish, increased internal breakdown and more rot development with unacceptable firmness retention for additional handling. Apricots stored in 12 or 15 % CO2 retained firmness and displayed enhanced finish with reduced rots and very little internal breakdown with storage duration of 60 days. Color was much slower to develop in apricots stored in 12 or 15 % CO2 for all storage periods.




th America. This difference can probably be attributed to lower temperatures along the Russian A^8180^Concern for global warming has focused attention on the rob of tropical forests in the reduction of ambient CO2 levels and mitigation of climate change. Deforestation is a major land use change in the tropics, with forest resources undergoing degradation through the influence of logging and conversion to other uses. Land use change is a product of varied local and regional resource use policies. Management of forest resources is one such major temporal factor, influencing resource stability and the carbon pool. Under a given management policy, both the long period of forest growth, and the slow turnover and decay of the carbon pool, enhance the relevance of stand level management policies as cost-effective mechanisms mitigating climate change. Apart from regional level uncertainties like the nature of land use and the estimation of carbon storage in vegetation and soil, the carbon flux of tropical forests is greatly influenced by uncertainty in regenerative capacity of forests and in harvest and management policies. A case study from India is used to develop a transition matrix model of natural forest management, and to explore the economic implications of maintaining and expanding existing carbon sinks. The study further explores the significance of investments in additional carbon sink in plantation forests, given continued uncertainty in natural forest management.

2713^10^Waibel,A E^Peter,T^Carslaw,K S^Oelhaf,H^Wetzel,G^Crutzen,P J^Poschl,U^Tsias,A^Reimer,E^Fischer,H^1999^1^Arctic ozone loss due to denitrification^32^283^5410^2064-2069^^^^^26 Mar^^^^^8183
139^174^227^2532^3816^3817^3818^3819^ turnover and decay of the carbon pool, enhance the relevance of stand level management policies as cost-effective mechanisms mitigating climate change. Apart from regional level uncertainties like the nature of land use and the estimation of carbon storage in vegetation and soil, the carbon flux of tropical forests is greatly influenced by uncertainty in regenerative capacity of forests and in harvest and managA^8182^Measurements from the winter of 1994-95 indicating removal of total reactive nitrogen from the Arctic stratosphere by particle sedimentation were used to constrain a microphysical model. The model suggests that denitrification is caused predominantly by nitric acid trihydrate particles in small number densities. The denitrification is shown to increase Arctic ozone Loss substantially. Sensitivity studies indicate that the Arctic stratosphere is currently at a threshold of denitrification. This implies that future stratospheric cooling, induced by an increase in the anthropogenic carbon dioxide burden, is likely to enhance denitrification and to delay until late in the next century the return of Arctic stratospheric ozone to preindustrial values.

2714^6^Cox,P M^Betts,R A^Bunton,C B^Essery,R L H^Rowntree,P R^Smith,J^1999^1^The impact of new land surface physics on the GCM simulation of climate and climate sensitivity^198^15^3^183-203^^^^^Mar^^^^^8185
1167^179^243^2491^256^3820^3821^3822^3823^674^managA^8184^Recent improvements to the Hadley Centre climate model include the introduction of a new land surface scheme called "MOSES" (Met Office Surface Exchange Scheme). MOSES is built on the previous scheme, but incorporates in addition an interactive plant photosynthesis and conductance module, and a new soil thermodynamics scheme which simulates the freezing and melting of soil water, and takes account of the dependence of soil thermal characteristics on the frozen and unfrozen components. The impact of these new features is demonstrated by comparing 1 x CO2 and 2 x CO2 climate simulations carried out using the old (UKMO) and new (MOSES) land surface schemes. MOSES is found to improve the simulation of current climate. Soil water freezing tends to warm the high-latitude land in the northern Hemisphere during autumn and winter, whilst the increased soil water availability in MOSES alleviates a spurious summer drying in the mid-latitudes. The interactive canopy conductance responds directly to CO2, suppressing transpiration as the concentration increases and producing a significant enhancement of the warming due to the radiative effects of CO2 alone.

2715^3^Levis,S^Foley,J A^Pollard,D^1999^1^Potential high-latitude vegetation feedbacks on CO2-induced climate change^65^26^6^747-750^^^^^15 Mar^^^^^8187
314^3824^3825^55^660^905^ scheme which simulates the freezing and melting of soil water, and takes account of the dependence of soil thermal characteristics on the frozen and unfrozen components. The impact of these new features is demonstrated by comparing 1 x CO2 and 2 x CO2 climate simulations carried out using the old (UKMO) and new (MOSES) land surface schemes. MOSES is found to improve the simulation of current climate. Soil water freezing tends to warm the high-latitude land in the northern Hemisphere during autumn and winter, whilst the increased soil water availability in MOSES alleviates a spurious summer drying in the mid-latitudes. The interactive canopy conductance responds directly to CO2, suppressiA^8186^We use a fully coupled climate-vegetation model to examine the potential effects of changes in vegetation cover on simulations of CO2-induced climate change. We find that vegetation feedbacks, acting mainly through changes in surface albedo, enhance greenhouse warming in the northern high latitudes during spring and summer months. In spring and summer, land surfaces north of 45 degrees N are warmed by 3.3 and 1.7 degrees C by a doubling of CO2 alone; vegetation feedbacks produce an additional warming of between 1.1-1.6 and 0.4-0.5 degrees C, respectively. In winter, however, vegetation feedbacks appear to oppose the 5.6 degrees C radiative warming, particularly over Eurasia. These results demonstrate that vegetation feedbacks are potentially significant and must be included in assessments of anthropogenic climate change.

2716^2^Ellert,B H^Janzen,H H^1999^1^Short-term influence of tillage on CO2 fluxes from a semi-arid soil on the Canadian Prairies^370^50^1^21-32^^^^^15 Feb^^^^^8189 to CO2, suppressi251^2772^310^3826^3827^3828^534^68^e-vegetation model to examine the potential effects of changes in vegetation cover on simulations of CO2-induced climate change. We find that vegetation feedbacks, acting mainly through changes in surface albedo, enhance greenhouse warming in the northern high latitudes during spring and summer months. In spring and summer, land surfaces north of 45 degrees N are warmed by 3.3 and 1.7 degrees C by a doubling of CO2 alone; vegetation feedbacks produce an additional warming of between 1.1-1.6 and 0.4-0.5 degrees C, respectively. In winter, however, vegetation feedbacks appear to oppose the 5.6 degrees C radiative warming, particularly over Eurasia. These results demonstrate that vegetation feedbacks are potentially significant and must be included in assessments of anthropogenic climate change.

2716^2^Ellert,B H^Janzen,H H^1999^1^Short-term influence of tillage on CO2 fluxes from a semi-arid soil on the Canadian Prairies^370^50^1^21-32^^^^^15 Feb^^^^^8189 to CO2, suppressiA^8188^The flux of CO2 from soil determines the extent to which carbon (C) deposited as plant litter is retained in the soil. Retention of soil C is beneficial for soil physical, chemical and biological properties, and is essential if soils are to be used as a repository of C to mitigate atmospheric CO2 increases. Although tillage is assumed to have a major influence on soil C retention, the extent to which tillage enhances the transfer of soil C to the atmosphere is uncertain. We assessed the short-term (50 h) influence of tillage on CO2 fluxes from Chernozemic soils under a two-year wheat (Triticum aestivum L.)-summerfallow rotation in a semi-arid region of the Canadian Prairie, The tillage effect and its persistence were assessed by using a portable CO2 analyzer to record several temporal series of CO2 fluxes, along undisturbed and tilled transects, at successive time intervals (from -0.5 to 50 h) after a single pass with a heavy-duty cultivator. Immediately after tillage, CO2 fluxes along the tilled transects increased from 2 to 4-fold above pre-tillage fluxes, but the increases were short-lived and fluxes along undisturbed and tilled transects were again similar within 24 h of cultivation. Total amounts of CO2 released by a tillage operation were quantified by: 1. linear interpolations among successive fluxes along tilled and undisturbed transects, and 2. by fitting a model to successive differences between fluxes along the transects. Both methods estimated the amounts of tillage-susceptible CO2 to be in the range of 3.6-7.2 kg C ha(-1). The tillage-induced flush of CO2 was attributed mainly to enhanced transport of CO2 already in the soil, but enhanced production of CO2 by heterotrophic soil organisms also may have contributed to the flush. Regardless of the sources of CO2 released by single tillage operations, amounts of tillage-susceptible soil C were minor; even 10 passes with a cultivator would account for less than 5% of annual soil CO2 emissions or crop residue production in these cropping systems. Our study suggested that the short- term influence of tillage on the transfer of soil C to atmospheric CO2 is small under semi-arid conditions like those in southern Alberta, Canada. Crown copyright (C) 1999 Published by Elsevier Science B.V, All rights reserved.

2717^1^Kothavala,Z^1999^1^The duration and severity of drought over eastern Australia simulated by a coupled ocean-atmosphere GCM with a transient increase in CO2^393^14^4^243-252^^^^^^^^^^8191
1205^137^2095^2829^314^3829^937^982^le CO2 to be in the range of 3.6-7.2 kg C ha(-1). The tillage-induced flush of CO2 was attributed mainly to enhanced transport of CO2 already in the soil, but enhanced production of CO2 by heterotrophic soil organisms also may have contributed to the flush. Regardless of the sources of CO2 released by single tillage operations, amounts of tillage-susceptible soil C were minor; even 10 passes with a cultivator would account for less than 5% of annual soil CO2 emissions or crop residue production in these cropping systems. A^8190^The combined effects of precipitation and temperature simulated by a coupled ocean-atmosphere General Circulation Model that showed an El Nino-like pattern with a transient increase in CO2, was examined for its effects on drought over eastern Australia. The Palmer Drought Severity Index (PDSI) was applied to determine the duration and severity of drought over a 30- year period due to decreased precipitation over the region. Application of the PDSI, using monthly mean temperature and total monthly precipitation to the final 30 years of the transient CO2 simulation revealed more prolonged and more intense periods of drought under enhanced greenhouse conditions when compared to a similar time span of the present-day simulation. (C) 1999 Elsevier Science Ltd. All rights reserved.

2718^3^Saleska,S R^Harte,J^Torn,M S^1999^1^The effect of experimental ecosystem warming on CO2 fluxes in a montane meadow^127^5^2^125-141^^^^^Feb^^^^^8193
1262^130^209^2367^2865^3111^377^3830^454^673^in these cropping systems. A^8192^Climatic change is predicted to alter rates of soil respiration and assimilation of carbon by plants. Net loss of carbon from ecosystems would form a positive feedback enhancing anthropogenic global warming. We tested the effect of increased heat input, one of the most certain impacts of global warming, on net ecosystem carbon exchange in a Rocky Mountain montane meadow. Overhead heaters were used to increase the radiative heat flux into plots spanning a moisture and vegetation gradient. We measured net whole-ecosystem CO2 fluxes using a closed-path chamber system, relatively nondisturbing bases, and a simple model to compensate for both slow chamber leaks and the CO2 concentration-dependence of photosynthetic uptake, in 1993 and 1994. In 1994, we also measured soil respiration separately. The heating treatment altered the timing and magnitude of net carbon fluxes into the dry zone of the plots in 1993 (reducing uptake by approximate to 100 g carbon m(-2)), but had an undetectable effect on carbon fluxes into the moist zone. During a strong drought year (1994), heating altered the timing, but did not significantly alter the cumulative magnitude, of net carbon uptake in the dry zone. Soil respiration measurements showed that when differences were detected in dry zone carbon Fluxes, they were caused by changes in carbon input from photosynthesis, not by temperature-driven changes in carbon output from soil respiration. When differences were detected in dry-zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by a temperature-driven changes in carbon output from soil respiration. Regression analysis suggested that the reduction in carbon inputs from plants was due to a combination of two soil moisture effects: a direct physiological response to decreased soil moisture, and a shift in plant community composition from high-productivity species to low-productivity species that are more drought tolerant. These results partially support predictions that warming may cause net carbon losses from some terrestrial ecosystems. They also suggest, however, that changes in soil moisture caused by global warming may be as important in driving ecosystem response as the direct effects of increased soil temperature.

2719^7^Mathooko,F M^Mwaniki,M W^Nakatsuka,A^Shiomi,S^Kubo,Y^Inaba,A^Nakamura,R^1999^1^Expression characteristics of CS-ACS1, CS-ACS2 and CS-ACS3, three members of the 1-aminocyclopropane-1-carboxylate synthase gene family in cucumber (Cucumis sativus L.) fruit under carbon dioxide stress^231^40^2^164-172^^^^^Feb^^^^^8195
1211^2346^2459^3408^3831^3832^3833^3834^3835^3836^il respiration. Regression analysis suggested that the reduction in carbon inputs from plants was due to a combination of two soil moisture effects: a direct physiological response to decreased soil moisture, and a shift in plant community composition from high-productivity species to low-productivity species that are more drought tolerant. These results partially support predictions that warming may cause net cA^8194^Fire investigated the expression pattern of three 1- aminocyclopropane-1-carboxylate (ACC) synthase genes, CS-ACS1, CS-ACS2 and CS-ACS3 in cucumber (Cucumis sativus L.) fruit under CO2 stress. CO2 stress-induced ethylene production paralleled the accumulation of only CS-ACS1 transcripts which disappeared upon withdrawal of CO2. Cycloheximide inhibited the CO2 stress-induced ethylene production but superinduced the accumulation of CS-ACS1 transcript. At higher concentrations, cycloheximide also induced the accumulation of CS-ACS2 and CS- ACS3 transcripts. In the presence of CO2 and cycloheximide, the accumulation of CS-ACS2 transcript occurred within Ih, disappeared after 3h and increased greatly upon withdrawal of CO2. Inhibitors of protein kinase and types 1 and 2A protein phosphatases which inhibited and stimulated, respectively, CO2 stress-induced ethylene production had little effect on the expression of these genes. The results presented here identify CS-ACS1 as the main ACC synthase gene responsible for the increased ethylene biosynthesis in cucumber fruit under CO2 stress and suggest that this gene is a primary response gene and its expression is under negative control since it is expressed by treatment with cycloheximide. The results further suggest that the regulation of CO2 stress-induced ethylene biosynthesis by reversible protein phosphorylation does not result from enhanced ACC synthase transcription.

2720^2^Drake,S R^Elfving,D C^1999^1^Response of three strains of 'Gala' apples to high carbon dioxide prior to controlled atmosphere storage^401^53^1^16-21^^^^^Jan^^^^^8197
3837^ximide, the accumulation of CS-ACS2 transcript occurred within Ih, disappeared after 3h and increased greatly upon withdrawal of CO2. Inhibitors of protein kinase and types 1 and 2A protein phosphatases which inhibited and stimulated, respectively, CO2 stress-induced ethylene production had little effect on the expression of these genes. The results presented here identify CS-ACS1 as the main ACC synthase gene responsA^8196^The postharvest fruit quality of three strains ('Royal Gala: 'Imperial Gala' and 'Crimson Gala') of apples was evaluated over two or three storage seasons. To determine the influence of carbon dioxide treatment on storage quality, apples were stored in normal controlled atmosphere (1% O-2 & 1% CO2), or treated with 12% CO2 for 7 or 14 days prior to normal CA and evaluated after 90 or 150 days of storage. The use of 12% CO2 prior to storage helped to maintain firmness of 'Royal Gala' apples in 1 of 3 seasons. Firmness of 'Imperial Gala' and 'Crimson Gala' apples was not influenced by high CO2 treatment, regardless of storage season. Other quality factors (color, soluble solids, acidity and carbohydrates) were not influenced to the extent that high CO(2)would be a viable option for the quality enhancement of 'Gala' apples during storage, regardless of strain. Use of normal CA maintained 'Gala' apple quality for 150 days of storage. Harvest date had a major influence on 'Gala' apple quality. A delay of one week reduced firmness and acidity, but enhanced color and content of sucrose, glucose and fructose in 'Royal Gala: 'Imperial Gala' and 'Crimson Gala' apples.

2721^3^Yoshioka,T^Satoh,S^Yamasue,Y^1998^1^Effect of increased concentration of soil CO2 on intermittent flushes of seed germination in Echinochloa crus-galli var. crus-galli^9^21^12^1301-1306^^^^^Dec^^^^^8199
130^ated after 90 or 150 days of storage. The use of 12% CO2 prior to storage helped to maintain firmness of 'Royal Gala' apples in 1 of 3 seasons. Firmness of 'Imperial Gala' and 'Crimson Gala' apples was not influenced by high CO2 treatment, regardless of storage season. Other quality factors (color, soluble solids, acidity and carbohydrates) were not influenced to the extent that high CO(2)would be a viable option for the quality enhancement of 'Gala' apples during storage, regardless of strain. Use of normal CA maintained 'Gala' apple quality for 150 days of storage. Harvest date had a major influence on 'Gala' apple quality. A delay of oA^8198^Soil-buried seeds of barnyardgrass (Echinochloa crusgalli var. crus-galli) germinated from April to June in three intermittent flushes. The later two flushes of germination occurred after heavy rainfall. Carbon dioxide concentration in soil air transiently increased to 30 dm(3) m(-3) after the rainfall, probably due to the increase in soil temperature and water potential. Germination of exhumed seeds was stimulated by exposure to CO2 at 30 dm(3) m(-3). Fluctuating temperature, light, water, ethylene, and nitrate are known to promote seed germination in many species. However, of these environmental factors, within ranges found in the field, only CO2 was effective in enhancing the germination of barnyardgrass seeds. We conclude that soil CO2 is responsible for causing intermittent flushes of germination. Detection of vegetation gaps may be explained by the responsiveness of buried seeds to CO2.
ple quality for 150 days of storage. Harvest date had a major influence on 'Gala' apple quality. A delay of o2722^1^Pirjola,L^1999^1^Effects of the increased UV radiation and biogenic VOC emissions on ultrafine sulphate aerosol formation^402^30^3^355-367^^^^^Mar^^^^^8201
1077^1120^1435^3199^3402^344^3676^3838^3839^3840^rbon dioxide concentration in soil air transiently increased to 30 dm(3) m(-3) after the rainfall, probably due to the increase in soil temperature and water potential. Germination of exhumed seeds was stimulated by exposure to CO2 at 30 dm(3) m(-3). Fluctuating temperature, light, water, ethylene, and nitrate are known to promote seed germination in many species. However, of these environmental factors, within ranges found in the field, only CO2 was effective in enhancing the germination of barnyardgrass seeds. We conclude that soil CO2 is responsible for causing intermittent flushes of germination. Detection of vegetation gaps may be explained by the responsiveness of buried seeds to CO2.
ple quality for 150 days of storage. Harvest date had a major influence on 'Gala' apple quality. A delay of oA^8200^A sectional model (AEROFOR) for the formation of sulphuric acid-water particles has been developed. The model includes gas-phase chemistry and aerosol dynamics. An increased UV-B irradiation penetrating into the troposphere due to stratospheric ozone depletion causes via the SO2 oxidation route an enhanced nucleation potential for new H2SO4-H2O particles as well as the growth of particles to CCN size. Using AEROFOR we show that after a nucleation event the nucleated particle concentration is linearly dependent on increased UV-B irradiation with a positive slope. On the other hand, due to increased CO2 concentration photosynthetic rates of plants will increase, and it is likely that enhanced photosynthesis in forests will increase emissions of biogenic volatile organic compounds (BVOC) such as isoprene and monoterpenes, We show that the nucleated particle concentration decreases with increasing BVOC emission, but this dependence is not linear. We investigate the strength of these opposite effects and fit a straight line for such UV-B and BVOC conditions which yield a certain particle number density. The coupling between O-3, OH and particle concentrations as a function of UV-B and BVOC emission is also demonstrated. (C) 1999 Elsevier Science Ltd. All rights reserved.

2723^2^Angell,R^Svejcar,T^1999^1^A chamber design for measuring net CO2 exchange on rangeland^319^52^1^27-31^^^^^Jan^^^^^8203
1484^1588^2928^467^AEROFOR we show that after a nucleation event the nucleated particle concentration is linearly dependent on increased UV-B irradiation with a positive slope. On the other hand, due to increased CO2 concentration photosynthetic rates of plants will increase, and it is likely that enhanced photosynthesis in forests will increase emissions of biogenic volatile organic compounds (BVOC) such as isoprene and monoterpenes, We show that the nucleated particle concentration decreases with increasing BVOC emission, but this dependence is not linear. We investigate the strength of these opposite effects and fA^8202^Net carbon exchange of terrestrial ecosystems will likely change as atmospheric CO2 concentration increases, Currently, little is known of the annual dynamics or magnitude of CO2 flux on many native and agricultural ecosystems. Remoteness of many ecosystems has limited our ability to measure CO2 flux on undisturbed vegetation. Today, many plant ecologists have portable photosynthesis systems with which they make single- leaf photosynthesis measurements. Utility of this equipment is enhanced when canopy-level CO2 flux is also measured. We designed a portable 1-m(3) closed chamber for use in measuring CO2 exchange in short statured vegetation with widely varied canopy structure. The design includes external ductwork equipped with doors which are used to open the chamber for ventilation with outside air between measurements. The chamber was tested on a Wyoming big sagebrush (Artemisia tridentata ssp. Wyomingensis Nutt.)/Thurber's needlegrass (Stipa thurberiana Piper) community using 10 plots equally divided between shrub and interspace, The ductwork and doors provided adequate ventilation to allow consecutive measurements of CO2 nux without removing the chamber from the plot. The chamber could differentiate CO2 flux between plots with sagebrush and those with grass only, even at relatively low fluxes, Net CO2 uptake per unit ground area was greater (P = 0.04) on sagebrush-grass plots (7.6 +/- 1.4 mu mol m(-2) s(-1)) than on interspace plots without sagebrush (3.1 +/- 1.0 pmol m(-2) s(- 1)). Chamber and leaf temperature increased by an average of 0.5 and 1.2 degrees C, respectively, during measurements.

2724^3^Weerakoon,W M^Olszyk,D M^Moss,D N^1999^1^Effects of nitrogen nutrition on responses of rice seedlings to carbon dioxide^169^72^1^1-8^^^^^12 Jan^^^^^8205
1528^243^344^434^92^tilation with outside air between measurements. The chamber was tested on a Wyoming big sagebrush (Artemisia tridentata ssp. Wyomingensis Nutt.)/Thurber's needlegrass (Stipa thurberiana Piper) community using 10 plots equally diviA^8204^Global atmospheric CO2 concentration is increasing, likely increasing the productivity of crops as higher CO2 enhances plant photosynthesis. Responsiveness to nitrogen supply is an essential trait of modem rice cultivars, and may play a role in the response of rice cultivars to CO2. To determine the relationship between these two important production variables on young rice plants, seedlings of Oryza sativa L. 'IR72' and 'KDML 105' were exposed for 28 days after sowing to CO2 levels of 373, 545, 723 and 895 mu molmoI(-1), and 3 levels of nitrogen fertility. There were large increases in leaf CO2 assimilation and biomass production whereas leaf nitrogen concentration dropped sharply as CO2 increased from 373 to 545 mu mol mol(-l), with little additional effect from higher levels of CO2. Root and shoot biomass, and tiller number per plant increased with increasing nitrogen supply and with increasing atmospheric CO2 concentration. The biomass response to CO2 was slight at low N supply, but became dramatically greater as the N supply increased. Mean root/shoot ratio increased slightly as atmospheric CO2 concentration increased, but decreased sharply as nitrogen fertility rate increased. These results suggest that careful attention to nitrogen fertilization will be necessary for rice fanning to get the full benefit of any future increases in atmospheric CO2. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

2725^3^Leymarie,J^Lasceve,G^Vavasseur,A^1998^1^Interaction of stomatal responses to ABA and CO2 in Arabidopsis thaliana^92^25^7^785-791^^^^^^^^^^8207
1155^1754^2128^2389^281^312^383^3841^3842^546^and biomass production whereas leaf nitrogen concentration dropped sharply as CO2 increased from 373 to 545 mu mol mol(-l), with little additional effect from higher levels of CO2. Root and shoot biomass, and tiller number per plant increased with increasing nitrogen supply and with increasing atmospheric CO2 concentration. The biomass response to CO2 was slight at low N supply, but became dramatiA^8206^Stomatal responses to ABA and CO2 were investigated in Arabidopsis thaliana (L.) Heynh. wild-type and ABA insensitive mutants (abi1-1, abi2-1, abi1-1 abi2-1) at the whole plant and at the isolated epidermis levels. In wild-type plants, feeding roots with ABA (1-50 mu M) triggered a rapid drop in leaf conductance which levelled off during the following photoperiods, and strongly inhibited the increase in conductance induced by light. The rapid response was strongly inhibited in abi1-1, abi2-1 and abi1-1 abi2-1 double mutants, but a residual long-term decrease in leaf conductance was still observed. In wild-type plants, exogenous ABA strongly enhanced the response to CO2 removal. Conversely, in the absence of CO2 the effect of ABA was drastically reduced in epidermal strip experiments. These results reveal a strong interaction between sensing of ABA and CO2 in stomata of A. thaliana. Despite an initially wide stomatal aperture in abi-1, abi-2 and double mutant plants, their stomatal responses to light and CO2 removal were half those of wild-type plants. Moreover these responses were totally independent of the presence of ABA, suggesting that ABI1 and ABI2 are either directly involved in the interaction between the two signalling pathways or, alternatively located upstream of this point of interaction.

2726^3^Franchito,S H^Rao,V B^da Silva,R R^1998^1^A parameterization of radiative fluxes suitable for use in a statistical-dynamical model^403^69^1-2^23-38^^^^^^^^^^8209
174^273^3288^3348^3506^3843^3844^3845^633^659^double mutants, but a residual long-term decrease in leaf conductance was still observed. In wild-type plants, exogenous ABA strongly enhanced the response to CO2 removal. Conversely, in the absence of CO2 the effect of ABA was drastically reduced in epidermal strip experiments. These results reveal a strong interaction between sensing of ABA and CO2 in stomata of A. thaliana. Despite an initially wide stomatal aperture in abi-1, abi-2 and double mutant plants, their stomatal responses to light aA^8208^A parameterization of shortwave and longwave radiation fluxes derived from detailed radiative transfer models is included in a global primitive equation statistical-dynamical model (SDM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the shortwave and longwave radiation fluxes matches well with the observations. The SDM variables such as surface and 500hPa temperatures, zonal winds at 250hPa and 750 hPa, vertical velocity at 500 hPa and precipitation are also in good agreement with the observations. A comparison between the results obtained with the present SDM and those with the previous version of the model indicates that the model results improved when the parameterization of the radiative fluxes based on detailed radiative transfer models are included into the SDM. The SDM is used to investigate its response to the greenhouse effect. Sensitivity experiments regarding the doubling of CO2 and the changing of the cloud amount and height an performed. In the case 2xCO(2) the model results are consistent with those obtained from GCMs, showing a warming of the climate system. An enhancement of the greenhouse effect is also noted when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions. This suggests that the greenhouse effect overcomes the albedo effect in the polar latitudes and the opposite occurs in other regions. In all the experiments the changes in the surface temperature an larger near poles, mainly in the Southern Hemisphere.

2727^2^Rigler,E^Zechmeister-Boltenstern,S^1998^1^Influence of nitrogen and carbon dioxide on ethylene and methane production in two different forest soils^404^153^3^227-237^^^^^Nov^^^^^8211
1012^1809^2772^3319^374^3846^3847^433^441^739^ts response to the greenhouse effect. Sensitivity expA^8210^The impact of nitrogen and CO, on ethylene and methane production was investigated in two different forest soils. The soils were adjusted to a water tension of 30 kPa. Nitrogen was added in the form of KNO3 or (NH4)(2)SO4 and CO2 was added in 5 different concentrations. To half of the samples, C2H2 was added to inhibit ethylene uptake. After 0, 24, and 96 hours, ethylene and methane concentrations were measured by gas chromatography. Ethylene net production increased with increasing N and CO2 concentrations. In the presence of acetylene, ethylene production was unaffected by the investigated amendments. Therefore, we suppose that the increasing ethylene net production rates are due to decreasing ethylene uptake rates. In the deciduous forest soil, there was no ethylene net production rate, as uptake rates exceeded production rates. Methane net production rates in the spruce forest soil increased with increasing N additions possibly due to a lowered C:N ratio and a decreased methane oxidation. Ethylene production rates in the presence of acetylene were slightly enhanced. In the deciduous forest soil, methane uptake rates decreased with nitrogen possibly due to the inhibition of the methanemonooxygenase. CO2 seemed to increase methane production in the presence of acetylene but had no significant effect on methane net production. Acetylene might serve as a substrate for methanogenesis.

2728^5^Diaz,S^Cabido,M^Zak,M^Carretero,E M^Aranibar,J^1999^1^Plant functional traits, ecosystem structure and land-use history along a climatic gradient in central-western Argentina^42^10^5^651-660^^^^^Oct^^^^^8213
1030^146^1787^344^673^778^ppose that the increasing ethylene net production rates are due to decreasing ethylene uptake rates. In the deciduous forest soil, there was no ethylene net production rate, as uptake rates exceeded production rates. Methane net production rates in the spruce forest soil increased with increasing N additions possibly due to a lowered C:N ratio and a decreased methane oxidation. EthyleneA^8212^This paper deals with theoretical concepts, methodological steps, and case studies related to the use of plant functional traits in the assessment of vegetation responses to climate and land use. Trait-environment links are considered, and special emphasis is put on the links between vegetation structure and ecosystem function, and on the role of disturbance history in determining vegetation responses to land use at present. As a basis for discussion, published and new case studies from central-western Argentina are presented. Similar plant traits measured with different levels of precision are utilized in the description of ecosystem structure in different land-use situations along a steep regional climatic gradient. The general protocol followed in the case studies represents a data-driven, non-hierarchical, low-tech approach, that can be applied to a wide range of spatial scales, from plots to regions. Climatic factors (including extreme events and seasonality), disturbance frequency and intensity, and disturbance history are suggested as key factors to be considered in global comparisons of vegetation responses to land use and in predictive models of ecosystem dynamics.

2729^1^Kirschbaum,M U F^2000^1^Will changes in soil organic carbon act as a positive or negative feedback on global warming?^26^48^1^21-51^^^^^Jan^^^^^8215
1106^137^1375^19^2349^2367^344^3729^3848^55^determining vegetation responses to land use at present. As a basis for discussion, published and new case studies from central-western Argentina are presented. Similar plant traits measured with different levels of precision are utilized in the description of ecosystem structure in different land-use situations along a steep regional climatic gradient. The general protocol followed in the case studies represents a data-driven, non-hierarchical, low-tech approach, that can be applied to a wide range of spatial scales, from plots to regions. Climatic factors (including extreme events and seasonality), disturbance frequency and intensity,A^8214^The world's soils contain about 1500 Gt of organic carbon to a depth of 1m and a further 900 Gt from 1-2m. A change of total soil organic carbon by just 10% would thus be equivalent to all the anthropogenic CO2 emitted over 30 years. Warming is likely to increase both the rate of decomposition and net primary production (NPP), with a fraction of NPP forming new organic carbon. Evidence from various sources can be used to assess whether NPP or the rate of decomposition has the greater temperature sensitivity, and, hence, whether warming is likely to lead to an increase or decrease in soil organic carbon. Evidence is reviewed from laboratory-based incubations, field measurements of organic carbon storage, carbon isotope ratios and soil respiration with either naturally varying temperatures or after experimentally increasing soil temperatures. Estimates of terrestrial carbon stored at the Last Glacial Maximum are also reviewed. The review concludes that the temperature dependence of organic matter decomposition can be best described as: d(T) = exp[3.36 (T - 40)/(T + 31.79)] where d(T) is the normalised decomposition rate at temperature T (in degrees C). In this equation, decomposition rate is normalised to '1' at 40 degrees C. The review concludes by simulating the likely changes in soil organic carbon with warming. In summary, it appears likely that warming will have the effect of reducing soil organic carbon by stimulating decomposition rates more than NPP. However, increasing CO2 is likely to simultaneously have the effect of increasing soil organic carbon through increases in NPP. Any changes are also likely to be very slow. The net effect of changes in soil organic carbon on atmospheric CO2 loading over the next decades to centuries is, therefore, likely to be small.

2730^2^Raich,J W^Tufekciogul,A^2000^1^Vegetation and soil respiration: Correlations and controls^26^48^1^71-90^^^^^Jan^^^^^8217
1106^1135^1686^19^209^2362^3414^3849^520^524^ncludes that the temperature dependence of organic matter decompA^8216^Soil respiration rates vary significantly among major plant biomes, suggesting that vegetation type influences the rate of soil respiration. However, correlations among climatic factors, vegetation distributions, and soil respiration rates make cause-effect arguments difficult. Vegetation may affect soil respiration by influencing soil microclimate and structure, the quantity of detritus supplied to the soil, the quality of that detritus, and the overall rate of root respiration. At the global scale, soil respiration rates correlate positively with litterfall rates in forests, as previously reported, and with aboveground net primary productivity in grasslands, providing evidence of the importance of detritus supply. To determine the direction and magnitude of the effect of vegetation type on soil respiration, we collated data from published studies where soil respiration rates were measured simultaneously in two or more plant communities. We found no predictable differences in soil respiration between cropped and vegetation-free soils, between forested and cropped soils, or between grassland and cropped soils, possibly due to the diversity of crops and cropping systems included. Factors such as temperature, moisture availability, and substrate properties that simultaneously influence the production and consumption of organic matter are more important in controlling the overall rate of soil respiration than is vegetation type in most cases. However, coniferous forests had similar to 10% lower rates of soil respiration than did adjacent broad-leaved forests growing on the same soil type, and grasslands had, on average, similar to 20% higher soil respiration rates than did comparable forest stands, demonstrating that vegetation type does in some cases significantly affect rates of soil respiration.

2731^1^Hall,F G^1999^1^Introduction to special section: BOREAS in 1999: Experiment and science overview^278^104^D22^27627-27639^^^^^27 Nov^^^^^8219
174^1775^312^314^3429^3850^3851^416^660^669^espiration betweenA^8218^The goal of BOREAS is to improve our understanding of the interactions between the boreal forest biome and the atmosphere in order to clarify their roles in global change. This overview briefly reviews the science background and motivations for the Boreal Ecosystem-Atmosphere Study (BOREAS). The findings of the 27 papers in this journal special issue are reviewed. Important scientific results of the project to date are summarized, and future research directions are identified.

2732^6^Dixon,R K^Smith,J B^Brown,S^Masera,O^Mata,L J^Buksha,I^1999^1^Simulations of forest system response and feedbacks to global change: experiences and results from the US Country Studies Program^81^122^3^289-305^^^^^20 Oct^^^^^8221
1467^314^377^3852^454^611^633^738^893^894^icantly affect rates of soil respiration.

2731^1^Hall,F G^1999^1^Introduction to special section: BOREAS in 1999: Experiment and science overview^278^104^D22^27627-27639^^^^^27 Nov^^^^^8219
174^1775^312^314^3429^3850^3851^416^660^669^espiration betweenA^8220^Large shifts in the response and feedbacks of forest systems are implied by models and systems analysis driven by global change scenarios of general circulation models (GCMs). Prior climate change analyses and modeling efforts have been reported at a global scale in a few developed countries, but relatively few national assessments have been successfully completed in developing countries. Under the auspices of the U.S. Country Studies Program, analysts from 55 countries employed a common set of methods and models to characterize current carbon (C) pools in forests, future impacts of global change on forest distribution, and management options for conserving and sequestering carbon dioxide (CO2) in forest systems. The analysis revealed that the response and feedbacks of forest systems to global climate change will be profound in the 55 countries studied on five continents. Globally, forest vegetation and soils contain about 1146 Pg C, with approximately 37% of this C in low-latitude forests, 14% in mid-latitudes, and 49% at high latitudes. The impacts of future global change on forest distribution and productivity will be most significant at high latitudes, with more modest changes in distribution and productivity at low latitudes. Future opportunities to conserve and sequester CO2 in forest systems are potentially significant, but land-use practices and global change will influence the size of this C pool and CO2 sink. In the future, a greater proportion of forests at all latitudes could become a greenhouse gas (GHG) source if sustained management and conservation policies are not employed. The timing and magnitude of future changes in forest systems are dependent on global environmental factors (for example, global change, biogeochemical Sulphur and Nitrogen cycles), as well as on human factors such as demographics, economic growth, technology, and resource management policies. (C) 1999 Elsevier Science B.V. All rights reserved.
Pg C, with approximately 37% of this C in low-latitude forests, 14% in mid2733^6^Running,S W^Baldocchi,D D^Turner,D P^Gower,S T^Bakwin,P S^Hibbard,K A^1999^1^A global terrestrial monitoring network integrating tower fluxes, flask sampling, ecosystem modeling and EOS satellite data^102^70^1^108-127^^^^^Oct^^^^^8223
137^1660^174^2449^377^3802^3853^529^669^888^n forest systems are potentially significant, but land-use practices and global change will influence the size of this C pool and CO2 sink. In the future, a greater proportion of forests at all latitudes could become a greenhouse gas (GHG) source if sustained management and conservation policies are not employed. The timing and magnitude of future changes in forest systems are dependent on global environmental factors (for example, global change, biogeochemical Sulphur and Nitrogen cycles), as well as on human factors such as demographics, economic growth, technology, and resource management policies. (C) 1999 Elsevier Science B.V. All rights reserved.
Pg C, with approximately 37% of this C in low-latitude forests, 14% in midA^8222^Acurrate monitoring of global seals changes in the terrestrial biosphere has become acutely important as the scope of human impacts on biological systems and atmospheric chemistry grows. For example, the Kyoto Protocol of 1997 signals some of the dramatic socioeconomic and political decisions that may lie ahead concerning CO2 emissions and global carbon cycle impacts. These decisions will rely heavily on accurate measures of global biospheric changes (Schimel 1998; IGBP TCWG, 1998). An array of national and international programs have inaugurated global satellite observations, critical field measurements of carbon and water fluxes, and global model development for the purposes of beginning to monitor the biosphere. The detection by these programs of interannual variability of ecosystem fluxes and of longer term trends will permit early indication of fundamental biospheric changes which might otherwise go undetected until major biome conversion begins. This article describes a blueprint for more comprehensive coordination of the various flux measurement and modeling activities into a global terrestrial monitoring network that will have direct relevance to the political decision making of global change. (C) Elsevier Science Inc., 1999.





2735^3^Malhi,Y^Baldocchi,D D^Jarvis,P G^1999^1^The carbon balance of tropical, temperate and boreal forests^9^22^6^715-740^^^^^Jun^^^^^8227
1134^1660^2349^3854^3855^393^484^715^729^890^res of global biospheric changes (Schimel 1998; IGBP TCWG, 1998). An array of national and international programs have inaugurated global satellite observations, critical field measurements of carbon and water fluxes, and global model development for the purposes of beginning to monitor the biosphere. The detection by these programs of interannual variability of ecosystem fluxes and of longer term trends will permit early indication of fundamental biospheric changes which might otherwise go undetected until major biome conversion begins. This article describes a blueprint for more compreA^8226^Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle, In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case-study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of sob carbon stocks.
es a blueprint for more compre2736^3^Ewert,F^van Oijen,M^Porter,J R^1999^1^Simulation of growth and development processes of spring wheat in response to CO2 and ozone for different sites and years in Europe using mechanistic crop simulation models^314^10^3-4^231-247^^^^^Apr^^^^^8229
1510^227^2290^243^417^434^58^724^728^73^have a large impact on the global carbon cycle, In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case-study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of sob carbon stocks.
es a blueprint for more compreA^8228^The response of crop growth and yield to CO2 and ozone is known to depend on climatic conditions and is difficult to quantify due to the complexity of the processes involved. Two modified mechanistic crop simulation models (AFRCWHEAT2-O3 and LINTULCC), which differ in the levels of mechanistic detail, were used to simulate the effects of CO2 (ambient, ambient x2) and ozone (ambient, ambient x1.5) on growth and developmental processes of spring wheat in response to climatic conditions. Simulations were analysed using data from the ESPACE-wheat project in which spring wheat cv. Minaret was grown in open-top chambers at nine sites throughout Europe and for up to 3 years at each site. Both models closely predicted phenological development and the average measured biomass at maturity. However, intermediate growth variables such as biomass and leaf area index (LAI) at anthesis, seasonal accumulated photosynthetically active radiation intercepted by the crop (Sigma IPAR), the average seasonal light use efficiency (LUE) and the light saturated rate of flag leaf photosynthesis (A(sat)) were predicted differently and less accurately by the two models. The effect of CO2 on the final biomass was underestimated by AFRCWHEAT2-O3 due to its poor simulation of the effect of CO2 on tillering, and LAI.LINTULCC overestimated the response of biomass production to changes in CO2 level due to an overprediction of the effect of CO2 on LUE. The measured effect of ozone exposure on final biomass was predicted closely by the two models. The models also simulated the observed interactive effect of CO2 and ozone on biomass production. However, the effects of ozone on LAI, Sigma IPAR and A(sat) were simulated differently by the models and less accurately with LINTULCC for the ozone effects on LAI and Sigma IPAR. Predictions of the variation between sites and years of growth and development parameters and of their responses to CO2 and ozone were poor for both AFRCWHEAT2-O3 and LINTULCC. It was concluded that other factors than those considered in the models such as chamber design and soil properties may have affected the growth and development of cv. Minaret. An analysis of the relationships between growth parameters calculated from the simulations supported this conclusion. In order to apply models for global change impact assessment studies, the difficulties in simulating biomass production in response to CO2 need to be considered. We suggest that the simulation of leaf area dynamics deserves particular attention in this regard. (C) 1999 Elsevier Science B.V. All rights reserved.

2737^4^Rathgeber,C^Guiot,J^Roche,P^Tessier,L^1999^1^Quercus humilis increase of productivity in the Mediterranean area^374^56^3^211-219^^^^^Mar-Apr^^^^^8231
1103^1203^227^312^32^344^3856^3857^3858^512^zone effects on LAI and Sigma IPAR. Predictions of the variation between sites and years of growth and development parameters and of their responses to CO2 and ozone were poor for both AFRCWHEAT2-O3 and LINTULCC. It was concluded that other factors than those A^8230^Several recent studies have shown an increasing long-term growth trend for various forest tree species in western Europe. Nevertheless such studies have not yet, been performed in Mediterranean Europe. The aim of this work is to analyse changes in productivity of some Mediterranean forest ecosystems compared with other medioeuropean forest ecosystems. Sixteen Quercus humilis (Miller) populations were sampled in south-east France. Tree ring widths were measured for each tree according to three radius, and annual basal area increments were calculated. Two growth indexes (IP and IC) were calculated with two different standardization techniques, in order to remove age and interstation productivity effects. From the IP and IC indexes we can see that there was a productivity increase during the last century, this increase being evaluated at 100 % (IC index). These results indicate that the Mediterranean forest ecosystems have shown a high productivity increase over the last century, as have the medioeuropean forest ecosystems. The best hypothesis to explain this increasing long-term growth trend is a direct CO2 fertilization along with N deposition fertilization. ((C) Inra/Elsevier, Paris.).

2738^5^Petschel- Held,G^Schellnhuber,H J^Bruckner,T^Toth,F L^Hasselmann,K^1999^1^The tolerable windows approach: Theoretical and methodological foundations^50^41^3-4^303-331^^^^^Mar^^^^^8233
137^314^3859^3860^tions were sampled in south-east France. Tree ring widths were measured for each tree according to three radius, and annual basal area increments were calculated. Two growth indexes (IP and IC) were calculated with two different standardization techniques, in order to remove age and interstation productivity effects. From the IP and IC indexes we can see that there was a productivity increase during the last century, this increase being evaluated at 100 % (IC index). These results indicate that the Mediterranean forest ecosystems have shown a high productivity increase over the last century, as have the medioeuropeaA^8232^The tolerable windows (TW) approach is presented as a novel scheme for integrated assessment of climate change. The TW approach is based on the specification of a set of guardrails for climate evolution which refer to various climate-related attributes. These constraints, which define what we call tolerable windows, can be purely systemic in nature - like critical thresholds for the North Atlantic Deep Water formation - or of a normative type - like minimum standards for per- capita food production worldwide. Starting from this catalogue of knock-out criteria and using appropriate modeling techniques, those policy strategies which are compatible with all the constraints specified are sought to be identified. In addition to the discussion of the basic elements and the general theory of the TW approach, a modeling exercise is carried out, based on simple models and assumptions adopted from the German Advisory Council on Global Change (WBGU). The analysis shows that if the global mean temperature is restricted to 2 degrees C beyond the preindustrial level, the cumulative emissions of CO2 are asymptotically limited to about 1550 Gt C. Yet the temporal distribution of these emissions is also determined by the climate and socio-economic constraints: using, for example, a maximal tolerable rate of temperature change of 0.2 degrees C/ dec and a smoothly varying emissions profile, we obtain the maximal cumulative emissions, amounting to 370 Gt C in 2050 and 585 Gt C in 2100.

2739^3^Weishampel,J F^Knox,R G^Levine,E R^1999^1^Soil saturation effects on forest dynamics: scaling across a southern boreal/northern hardwood landscape^70^14^2^121-135^^^^^Apr^^^^^8235
130^146^1689^2605^3861^3862^51^611^672^939^to be identified. In addition to the discussion of the basic elements and the general theory of the TW approach, a modeling exercise is carried out, based on simple models and assumptions adopted from the German Advisory Council on Global Change (WBGU). The analysis shows that if the global mean temperature is restA^8234^Patch modeling can be used to scale-up processes to portray landscape-level dynamics. Via direct extrapolation, a heterogeneous landscape is divided into its constituent patches; dynamics are simulated on each representative patch and are weighted and aggregated to formulate the higher level response. Further extrapolation may be attained by coarsening the resolution of or lumping environmental data (e.g., climatic, edaphic, hydrologic, topographic) used to delimit a patch. Forest patterns at the southern boreal/northern hardwood transition zone are often defined by soil heterogeneity, determined primarily by the extent and duration of soil saturation. To determine how landscape-level dynamics predicted from direct extrapolation compare when coarsening soil parameters, we simulated forest dynamics for soil series representing a range of drainage classes from east-central Maine. Responses were aggregated according to the distribution of soil associations comprising a 600 ha area based on local- (1.12,000), county- (1:120,000) and state- (1:250,000) scale soil maps. At the patch level, simulated aboveground biomass accumulated more slowly in poorer draining soils. Different soil series yielded different communities comprised of species with various tolerances for soil saturation. When aggregated, removal of waterlogging caused a 20-60% increase in biomass accumulation during the first 50 years of simulation. However, this early successional increase and the maximum level of biomass accumulation over a 200 year period varied by as much as 40% depending on the geospatial data. This marked discrepancy suggests caution when extrapolating with forest patch models by coarsening parameters and demonstrates how rules used to rescale environmental data need to be evaluated for consistency.

2740^5^Nemry,B^Francois,L^Gerard,J C^Bondeau,A^Heimann,M^1999^1^Comparing global models of terrestrial net primary productivity (NPP): analysis of the seasonal atmospheric CO2 signal^127^5^^65-76^^^^^Apr^^^^^8237 local- (1.12,0312^3863^529^543^661^673^nd state- (1:250,000) scale soil maps. At the patch level, simulated aboveground biomass accumulated more slowly in poorer draining soils. Different soil series yielded different communities comprised of species with various tolerances for soil saturation. When aggregated, removal of waterlogging caused a 20-60% increase in biomass accumulation during the first 50 years of simulation. However, this early successional increase and the maximum level of biomass accumulation over a 200 year period varied by as much as 40% depending on the geospatial data. This marked discrepancy suggests caution when extrapolating with forest patch models by coarsening parameters and demonstrates how rules used to rescale environmental data need to be evaluated for consistency.

2740^5^Nemry,B^Francois,L^Gerard,J C^Bondeau,A^Heimann,M^1999^1^Comparing global models of terrestrial net primary productivity (NPP): analysis of the seasonal atmospheric CO2 signal^127^5^^65-76^^^^^Apr^^^^^8237 local- (1.12,0A^8236^Eight terrestrial biospheric models (TBMs) calculating the monthly distributions of both net primary productivity (NPP) and soil heterotrophic respiration (R-H) in the Potsdam NPP Model Intercomparison workshop are used to simulate seasonal patterns of atmospheric CO2 concentration. For each model, we used net ecosystem productivity (NEP=NPP-R-H) as the source function in the TM2 atmospheric transport model from the Max- Planck Institute for Meteorology. Comparing the simulated concentration fields with detrended measurements from 25 monitoring stations spread over the world, we found that the decreasing seasonal amplitude from north to south is rather well reproduced by all the models, though the amplitudes are slightly too low in the north. The agreement between the simulated and observed seasonality is good in the northern hemisphere, but poor in the southern hemisphere, even when the ocean is accounted for. Based on a Fourier analysis of the calculated zonal atmospheric signals, tropical NEP plays a key role in the seasonal cycle of the atmospheric CO2 in the whole southern hemisphere. The relatively poor match between measured and predicted atmospheric CO2 in this hemisphere suggests problems with all the models. The simulation of water relations, a dominant regulator of NEP in the tropics, is a leading candidate for the source of these problems.

2741^1^Delmas,R J^1998^1^Ice-core records of global climate and environment changes^405^107^4^307-319^^^^^Dec^^^^^8239
2369^3261^3318^3864^3865^3866^3867^3868^3869^661^asurements from 25 monitoring stations spread over the world, we found that the decreasing seasonal amplitude from north to south is rather well reproduced by all the models, though the amplitudes are slightly too low in the north. The agreement between the simulated and observed seasonality is good in the northern hemisphere, but poor in the southern hemisphere, even when the ocean is accounted for. Based on a Fourier analysis of the calculated zonal atmospheric signals, tropical NEP playsA^8238^Precipitation accumulating on the Greenland and Antarctic ice sheets records several key parameters (temperature, accumulation, composition of atmospheric gases and aerosols) of primary interest for documenting the past global environment over recent climatic cycles and the chemistry of the preindustrial, atmosphere. Several deep ice cores from Antarctica and Greenland have been studied over the last fifteen years. In both hemispheres, temperature records (based on stable isotope measurements in water) show the succession of glacial and interglacial periods. However, detailed features of the climatic stages are not identical in Antarctica and in Greenland. A tight link between global climate and greenhouse gas concentrations was discovered, CO2 and CH4 concentrations being lower in glacial conditions by about 80 and 0.3 ppmv, respectively, with respect to their pre-industrial levels of 280 and 0.65 ppmv. Coldest stages are also characterized by higher sea-salt and crustal aerosol concentrations. In Greenland, contrary to Antarctica, ice-age ice is alkaline. Gas-derived aerosol (in particular, sulfate) concentrations are generally higher for glacial periods, but not similar in both the hemispheres. Marine and continental biomass-related species are significant in Antarctica and Greenland ice, respectively. Finally, the growing impact of anthropogenic activities on the atmospheric composition is well recorded in both polar regions for long-lived compounds (in particular greenhouse gases), but mostly in Greenland for short-lived pollutants.

2742^2^Brown,R A^Rosenberg,N J^1999^1^Climate change impacts on the potential productivity of corn and winter wheat in their primary United States growing regions^50^41^1^73-107^^^^^Jan^^^^^8241
1138^1139^1356^174^374^377^3870^434^51^633^ng lower in glacial conditions by about 80 and 0.3 ppmv, respectively, with respect to their pre-industrial levels of 280 and 0.65 ppmv. Coldest stages are also characterized by higher sea-salt and crustal aerosol concentrations. In GrA^8240^We calculate the impacts of climate effects inferred from three atmospheric general circulation models (GCMs) at three levels of climate change severity associated with change in global mean temperature (GMT) of 1.0, 2.5 and 5.0 degrees C and three levels of atmospheric CO2 concentration ([CO2]) - 365 (no CO2 fertilization effect), 560 and 750 ppm - on the potential production of dryland winter wheat (Triticum aestivum L.) and corn (Zea mays L.) for the primary (current) U.S. growing regions of each crop. This analysis is a subset of the Global Change Assessment Model (GCAM) which has the goal of integrating the linkages and feedbacks among human activities and resulting greenhouse gas emissions, changes in atmospheric composition and resulting climate change, and impacts on terrestrial systems. A set of representative farms was designed for each of the primary production regions studied and the Erosion Productivity Impact Calculator (EPIC) was used to simulate crop response to climate change. The GCMs applied were the Goddard Institute of Space Studies (GISS), the United Kingdom Meteorological Transient (UKTR) and the Australian Bureau of Meteorological Research Center (BMRC), each regionalized by means of a scenario generator (SCENGEN). The GISS scenarios have the least impact on corn and wheat production, reducing national potential production for corn by 6% and wheat by 7% at a GMT of 2.5 degrees C and no CO2 fertilization effect, the UKTR scenario had the most severe impact on wheat, reducing production by 18% under the same conditions; BMRC had the greatest negative impact on corn, reducing produc tion by 20%. A GMT increase of 1.0 degrees marginally decreased corn and wheat production. Increasing GMT had a detrimental impact on both corn and wheat production, with wheat production suffering the greatest losses. Decreases for wheat production at GMT 5.0 and [CO2] = 365 ppm range from 36% for the GISS to 76% for the UKTR scenario. Increases in atmospheric [CO2] had a positive impact on both corn and wheat production. AT GMT 1.0, an increase in [CO2] to 560 ppm resulted in a net increase in corn and wheat production above baseline levels (from 18 to 29% for wheat and 2 to 5% for corn). Increases in [CO2] help to offset yield reductions at higher GMT levels; in most cases, however, these increases are not sufficient to return crop production to baseline levels.

2743^4^Christensen,T R^Jonasson,S^Callaghan,T V^Havstrom,M^1999^1^On the potential CO2 release from tundra soils in a changing climate^406^11^2-3^127-134^^^^^Feb^^^^^8243
1986^2137^377^681^d the greatest negative impact on corn, reducing produc tion by 20%. A GMT increase of 1.0 degrees marginally decreased corn and wheat production. Increasing GMT had a detrimental impact on both corn and wheat production, with wheat production suffering the greatest losses. Decreases for wheat production at GMT 5.0 and [CO2] = 365 ppm range from 36% for the GISS to 76% for the UKTR scenario. Increases in atmospheric [CO2] had a positive impact on both corn andA^8242^About 30% of the carbon in terrestrial ecosystems is stored in northern wetlands and boreal forest regions. Prevailing cold and wet soil conditions have largely been responsible for this carbon accumulation. It has been suggested that a warmer and drier climate in these regions might increase the decomposition rate and, hence, release more CO2 to the atmosphere than at present. This study reports on the spatial variability and temperature dependence of the potential carbon release after incubating highly organic soils from the European Arctic and Siberia at different temperatures. We found that the decay potential, measured as CO2 production in laboratory experiments, differed strongly within and among sites, particularly at higher soil temperatures. Furthermore, both the decay potential and its temperature response decreased significantly with depth in the soil, presumably because the older soils at deeper layers contained higher proportions of recalcitrant carbon than the younger soil organic matter at the surface. These results have implications for global models of potential feedbacks on climate change inferred from changes in the carbon balance of northern wetlands and tundra. Firstly, because the decay potential of the organic matter varies locally as well as regionally, predictions of how the tundra carbon balance may change will be unreliable if these are based on measurements at a few sites only. Secondly, any increase in CO2 production may be transitional as both the carbon flux and its temperature sensitivity decrease when the most easily degradable organic material near the soil surface has decomposed. Consequently, it is crucial to account for transient responses and regional differences in the models of potential feedbacks on climate change from changed carbon cycling in northern terrestrial ecosystems. (C) 1999 Elsevier Science B.V.
epth in the soil, presumably because the older soils at deeper layers contained higher proportions of recalcitrant carbon than the younger soil organic matter2744^34^Hutjes,R W A^Kabat,P^Running,S W^Shuttleworth,W J^Field,C^Bass,B^Dias,M A F D^Avissar,R^Becker,A^Claussen,M^Dolman,A J^Feddes,R A^Fosberg,M^Fukushima,Y^Gash,J H C^Guenni,L^Hoff,H^Jarvis,P G^Kayane,I^Krenke,A N^Liu,C^Meybeck,M^Nobre,C A^Oyebande,L^Pitman,A^Pielke,R A^Raupach,M^Saugier,B^Schulze,E D^Sellers,P J^Tenhunen,J D^Valentini,R^Victoria,R L^Vorosmarty,C J^1998^1^Biospheric aspects of the hydrological cycle - Preface^218^213^1-4^1-21^^^^^Dec^^^^^8245
1484^187^344^3871^3872^3873^514^659^673^715^ture sensitivity decrease when the most easily degradable organic material near the soil surface has decomposed. Consequently, it is crucial to account for transient responses and regional differences in the models of potential feedbacks on climate change from changed carbon cycling in northern terrestrial ecosystems. (C) 1999 Elsevier Science B.V.
epth in the soil, presumably because the older soils at deeper layers contained higher proportions of recalcitrant carbon than the younger soil organic matterA^8244^The Core Project Biospheric Aspects of the Hydrological Cycle (BAHC) of the International Geosphere Biosphere Programme (IGBP) addresses the biospheric aspects of the hydrological cycle through experiments and modelling of energy, water, carbon dioxide and sediment fluxes in the soil-vegetation- atmosphere system at a variety of spatial and temporal scales. Active regulation of water, energy and carbon dioxide fluxes by the vegetation make it an important factor in regulating the Earth's hydrological cycle and in the formation of the climate. Consequently, human induced conversion of vegetation cover is an important driver for climate change. A number of recent studies, discussed in this paper, emphasise the importance of the terrestrial biosphere for the climate system. Initially, these studies demonstrate the influence of the land surface on tropical weather and climate, revealing the mechanisms, acting at various scales, that connect increasing temperatures and decreasing rainfall to large-scale deforestation and other forms of land degradation. More recently, the significance of the land surface processes for water cycle and for weather and climate in temperate and boreal zones was demonstrated. In addition the terrestrial biosphere plays a significant role in the carbon dioxide fluxes and in global carbon balance. Recent work suggests that many ecosystems both in the tropics and in temperate zones may act as a substantial sink for carbon dioxide, though the temporal variability of this sink strength is yet unclear. Further, carbon dioxide uptake and evaporation by vegetation are intrinsically coupled leading to Links and feedbacks between land surface and climate that are hardly explored yet. Earth's vegetation cover and its changes owing to human impact have a profound influence on a lateral redistribution of water and transported constituents, such as nutrients and sediments, and acts therefore as an important moderator of Earth's biogeochemical cycles. In the BAHC science programme, the importance of studying the influence of climate and human activities on mobilisation and river-borne transport of constituents is explicitly articulated. The terrestrial water and associated material cycles are studied as highly dynamic in space and time, and reflect a complex interplay among climatic forcing, topography, land cover and vegetation dynamics. Despite a large progress in our understanding of how the terrestrial biosphere interacts with Earth's and climate system and with the terrestrial part of its hydrological cycle, a number of basic issues still remain unresolved. Limited to the scope of BAHC, the paper briefly assesses the present status and identifies the most important outstanding issues, which require further research. Two, arguably most important outstanding issues are identified: a limited understanding of natural variability, especially with respect to seasonal to inter-annual cycles, and of a complex ecosystem behaviour resulting from multiple feedbacks and multiple coupled biogeochemical cycles within the overall climate system. This leads to two major challenges for the future science agenda related to global change research. First, there is a need for a strong multidisciplinary integration of research efforts in both modelling and experiments, the latter extending to inter- annual timescales. Second, the ever increasing complexity in characterisation and modelling of the climate system, which is mainly owing to incorporation of the biosphere's and human feedbacks, may call for a new approach in global change impact studies. Methodologies need to be developed to identify risks to, and vulnerability of environmental systems, taking into account all important interactions between atmospheric, ecological and hydrological processes at relevant scales. With respect to the influence of climate and human activities on mobilisation and river-borne transport of constituents, the main issues for the future are related to declining availability and quality of ground data for quantity and quality of water discharge. Such assessments presented in this paper, in combination with community wide science evaluation, has lead to an update of the science agenda for BAHC, a summary of which is provided in the appendix. (C) 1998 Elsevier Science B.V. All rights reserved.

tter extending to inter- annual timescales. Second, the ever increasing complexity in characterisation and modelling of the climate system, which is mainly owing to incorporation of the biosphere's and human feedbacks, may call for a new approach in global change impact studies. Methodologies need to be developed to identify risks to, and vulnerability of environmental systems, taking into account all important interactions between atmospheric, ecological and hydrological processes at relevant scales. With respect to the influence of climate and human activities on mobilisation and river-borne transport of constituents, the main issues for the future are related to declining availability and quality of ground data for quantity and quality of water