Temperature sensitivity of soil respiration in relation to soil moisture in 11 communities of typical temperate steppe in Inner Mongolia
典型温带草原群落土壤呼吸温度敏感性与土壤水分的关系

Atmospheric concentrations of greenhouse gases have increased dramatically since the beginning of industrial revolution due to human activities such as fossil fuel combustion and land-use change. Because of the increasing atmospheric concentrations of greenhouse gases and their greenhouse effect, a recent IPCC report has predicted that a much warmer climate is coming. Carbon dioxide is one of the most concerned greenhouse gases in the study of global climate change. Because soil respiration is a major process that controls and influences atmospheric CO_2 concentration, response of soil respiration to temperature changes has become a focal point in studies of the global carbon cycle. In addition to temperature soil moisture is another important factor that affects soil respiration. While many studies have shown that temperature exerts a major control on soil respiration, the relationship between temperature sensitivity of soil respiration (often expressed as Q _(10)) and soil moisture conditions is rarely investigated. Using the alkali absorption technique, we measured soil CO_2 efflux in 11 temperate steppe communities in Xilin River basin, Inner Mongolia. We calculated the Q _(10) values of soil respiration in the 11 communities, and then analyzed the sensitivity of Q _(10) to soil moisture content (0~20cm). Among the 11 communities, Q _(10) values varied from 1.47 to 1.84, with a mean value of 1.65 and a coefficient of variation of 6.94%. Using the Spearman's Rank-Order correlation method, we also analyze the relationship between Q _(10) values and soil moisture content, and found that Q _(10) values were positively correlated to average surface soil moisture ( R =0.64545, p =0.032), indicating that soil moisture significantly affected soil respiration. Our results showed that the spring wheat field had the greatest Q _(10) value (1.84), followed by the wet mixed grasses ( Q _(10)=1.78). Whereas, the Artemisia frigida -Potentilla acaulis community, had the lowest Q _(10) value (1.47). In the typical temperate steppe, soil temperature tends to have greater impact on soil respiration in wetter habitats than in drier habitats. This also implies that any significant change in the spatio-temporal pattern of soil moisture can have significant effects on soil respiration in the temperate steppe of China, and, therefore, the effect of soil moisture should be taken into account when soil CO_2 efflux is to be modeled on a larger spatial and temporal scale.