responses of photosynthetic capacity to soil moisture gradient in perennial rhizome grass and perennial bunchgrass反应光合能力的土壤水分梯度的多年生根茎多年生草和bunchgrass.pdf

Xu and Zhou BMC Plant Biology 2011, 11:21 /1471-2229/11/21 RESEARCH ARTICLE Open Access Responses of photosynthetic capacity to soil moisture gradient in perennial rhizome grass and perennial bunchgrass 1 1,2* Zhenzhu Xu , Guangsheng Zhou Abstract Background: Changing water condition represents a dramatic impact on global terrestrial ecosystem productivity, mainly by limiting plant functions, including growth and photosynthesis, particularly in arid and semiarid areas. However, responses of the potential photosynthetic capacity to soil water status in a wide range of soil moisture levels, and determination of their thresholds are poorly understood. This study examined the response patterns of plant photosynthetic capacity and their thresholds to a soil moisture gradient in a perennial rhizome grass, Leymus chinensis, and a perennial bunchgrass, Stipa grandis, both dominant in the Eurasian Steppe. Results: Severe water deficit produced negative effects on light-saturated net CO2 assimilation rate (Asat), stomatal conductance (gs), mesophyll conductance (gm), maximum carboxylation velocity (Vc,max), and maximal efficiency of PSII photochemistry (Fv/Fm). Photosynthetic activity was enhanced under moderate soil moisture with reductions under both severe water deficit and excessive water conditions, which may represent the response patterns of plant growth and photosynthetic capacity to the soil water gradient. Our results also showed that S. grandis had lower productivity and photosynthetic potentials under moderate water status, although it demonstrated generally similar relationship patterns between photosynthetic potentials and water status relative to L. chinensis. Conclusions: The experiments tested and confirmed the hypothesis that responsive threshold points appear when