Response of ecosystem respiration to soil water and plant biomass in a semiarid grassland

The Mongolian steppe zone constitutes a major part of East Asian grasslands. The objective of this study was to evaluate the quantitative dependence of ecosystem respiration (R-eco) on the environmental variables of soil water and plant biomass in a semiarid grassland ecosystem. We determined R-eco using opaque, closed chambers in a Mongolian grassland dominated by graminaceous perennial grasses during six periods: July 2004, May 2005, July 2005, September 2005, June 2006, and August 2009. Using the data collected when soil water content and aboveground biomass were relatively constant, values of R-eco were fitted to an exponential temperature function, and the standardized rate of R-eco at 20 degrees C (R-20) and temperature sensitivity (Q(10)) of R-eco were calculated for each measurement plot and period. The results indicate that aboveground biomass significantly affected the variation in R-20, and the relationship was expressed with a linear model. The R-20 residuals of the linear biomass model were highly correlated with soil water content by a quadratic function. The Q(10) values showed a weak positive relationship with soil water content. Temporal and spatial variations in R-eco were well predicted by the exponential temperature model with R-20, which relates to aboveground biomass and soil water content, and with Q(10), which relates to soil water content.