Soil moisture effect on the temperature dependence of ecosystem respiration in a subtropical Pinus plantation of southeastern China

Variation in temperature accounts for most of the seasonal fluctuation of terrestrial ecosystem respiration. However, other factors, such as soil moisture, also influence ecosystem respiration. In this study, continuous measurement of carbon dioxide exchange was made over a subtropical Pinus plantation of southeastern China using the eddy covariance (EC) technique. The effect of soil water content on ecosystem respiration and its sensitivity to temperature (Q10) were examined during the unusual dry summer of 2003. The results indicate that soil water content significantly affected the dynamics of respiration rate and its relationship with temperature in the drought-stressed ecosystem. The effect of soil water content on the Q10 value of ecosystem respiration is described best by a quadratic function, instead of the commonly used multiplicative model. The regression model analysis revealed that ecosystem respiration was more sensitive to soil water content than is estimated by the multiplicative model. The multiplicative model led to an overestimation of response of the respiration to warming under the dry soil condition. Sensitivity of the ecosystem respiration to temperature was found to vary with air temperature and soil water content. This, to a considerable extent, precludes accurate estimates of the seasonal dynamics of ecosystem respiration.