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Effect of Elevated CO_2 and Drought on Soil Microbial Communities Associated with Andropogon gerardii

Journal of Integrative Plant Biology 2008年第11期50卷 1406-1415页

作者： Issmat I. Kassem puneet joshi Yon Sigler Scott Heckathorn Qi Wang Department of Environmental Sciences University of Toledo Ohio 43606 USA Department of Civil Engineering University of Toledo Ohio 43606 USA

Our understanding of the effects of elevated atmospheric CO2, singly and in combination with other environmental changes, on plant-soil interactions is incomplete. Elevated CO2 effects on C4 plants, though smaller than on C3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO2 and drought on soil microbial communities associated with a dominant C4 prairie grass, Andropogon gerardii Vitman. Elevated CO2 and drought both affected resources available to the soil microbial community. For example, elevated CO2 increased the soil C：N ratio and water content during drought, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO2 increased biomass while ameliorating biomass decreases that were induced under drought. Total and active direct bacterial counts and carbon substrate use （overall use and number of used sources） increased significantly under elevated CO2. Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO2, singly and combined, did not affect the soil bacteria community structure. We conclude that elevated CO2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO2 also limited drought-related impacts on microbial activity and biomass, which likely resulted from decreased plant water use under elevated CO2. These are among the first results showing that elevated CO2 and drought work in opposition to modulate plant-associated soil-bacteria responses, which should then influence soil resources and plant and ecosystem function.

关键词： denaturing gradient gel electrophoresis drought elevated CO2 soil microbial communities.

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Interactive Effects of Elevated CO_2 and Growth Temperature on the Tolerance of Photosynthesis to Acute Heat Stress in C_3 and C_4 Species

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Journal of Integrative Plant Biology 2008年第11期50卷 1375-1387页

作者： E. William Hamilton III Scott A. Heckathorn puneet joshi Dan Wang Deepak Barua Department of Biology Washington and Lee University Lexington Virginia USA Department of Environmental Sciences University of Toledo Toledo Ohio USA

Determining effects of elevated CO2 on the tolerance of photosynthesis to acute heat-stress （heat wave） is necessary for predicting plant responses to global warming, as photosynthesis is thermolabile and acute heat-stress and atmospheric CO2 will increase in the future. Few studies have examined this, and past results are variable, which may be due to methodological variation. To address this, we grew two C3 and two C4 species at current or elevated CO2 and three different growth temperatures （GT）. We assessed photosynthetic thermotolerance in both unacclimated （basal tolerance） and preheat-stressed （preHS = acclimated） plants. In C3 species, basal thermotolerance of net photosynthesis （Pn） was increased in high CO2, but in C4 species, Pn thermotlerance was decreased by high CO2 （except Zea mays at low GT）; CO2 effects in preHS plants were mostly small or absent, though high CO2 was detrimental in one C3 and one C4 species at warmer GT. Though high CO2 generally decreased stomatal conductance, decreases in P, during heat stress were mostly due to non-stomatal effects. Photosystem Ⅱ （PSⅡ） efficiency was often decreased by high CO2 during heat stress, especially at high GT; CO2 effects on post-PSⅡ electron transport were variable. Thus, high CO2 often affected photosynthetic theromotolerance, and the effects varied with photosynthetic pathway, growth temperature, and acclimation state. Most importantly, in heat-stressed plants at normal or warmer growth temperatures, high CO2 may often decrease, or not benefit as expected, tolerance of photosynthesis to acute heat stress. Therefore, interactive effects of elevated CO2 and warmer growth temperatures on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.

关键词： carbon dioxide global climate change photosynthesis thermotolerance.

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Interactive Effects of Elevated CO_2 and Ozone on Leaf Thermotolerance in Field-grown Glycine max

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Journal of Integrative Plant Biology 2008年第11期50卷 1396-1405页

作者： Sasmita Mishra Scott A. Heckathorn Deepak Barua Dan Wang puneet joshi E. William Hamilton III Jonathan Frantz Department of Environmental Sciences University of Toledo Toledo Ohio USA Department of Biology Washington and Lee University Lexington Virginia USA United States Department of Agricuffure-Agricultural Research Service University of Toledo Toledo Ohio 43606 USA

Humans are increasing atmospheric CO2, ground-level ozone （O3）, and mean and acute high temperatures. Laboratory studies show that elevated CO2 can increase thermotolerance of photosynthesis in C3 plants. O3-related oxidative stress may offset benefits of elevated CO2 during heat-waves. We determined effects of elevated CO2 and O3 on leaf thermotolerance of field-grown Glycine max （soybean, C3）. Photosynthetic electron transport （Фet） was measured in attached leaves heated in situ and detached leaves heated under ambient CO2 and O3. Heating decreased Фet, which O3 exacerbated. Elevated CO2 prevented O3-related decreases during heating, but only increased Фet under ambient O3 in the field. Heating decreased chlorophyll and carotenoids, especially under elevated CO2. Neither CO2 nor O3 affected heat-shock proteins. Heating increased catalase （except in high O3） and Cu/Zn-superoxide dismutase （SOD）, but not Mn- SOD; CO2 and O3 decreased catalase but neither SOD. Soluble carbohydrates were unaffected by heating, but increased in elevated CO2. Thus, protection of photosynthesis during heat stress by elevated CO2 occurs in field-grown soybean under ambient O3, as in the lab, and high CO2 limits heat damage under elevated O3, but this protection is likely from decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.

关键词： anti-oxidants global change heat-shock proteins photosynthesis.

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