Effect of land use change on soil respiration from freshwater marshes in northeast of China

The Sanjiang Plain is the largest low-altitudinal swampy plain in China where has been strongly affected by human activities particularly the conversion of marsh to cropland. Four plots of Carex lasiocarpa marsh, Deyeuxia angustifolia marsh, rice field and dryland were selected in this study to evaluate the effect of land-use change on soil respiration. Results showed that the seasonal changes of soil respiration rates from Carex lasiocarpa marsh and Deyeuxia angustifolia marsh were identical with single-peak. The largest values appeared in summer and the lowest ones appeared in winter. The seasonal variation of soil respiration rate from dryland was the same as the marshland, but the seasonal course of soil respiration rate from rice field changed and the peak values postponed in autumn. The carbon effluxes by soil respiration from Carex lasiocarpa marsh, Deyeuxia angustifolia marsh, dryland and rice field were 3.14+/-0.45, 4.81+/-0.68, 2.85+/-0.38 and 2.18+/-0.31 tC ha(-1) . yr(-1), respectively. Significant relationships were found between temperature and soil respiration rate from Carex lasiocarpa marsh, Deyeuxia angustifolia marsh and dryland, and Q(10) values were 2.1, 2.5 and 1.8, respectively. The relationships between soil respiration rate and soil moisture/water table were best described by quadratic equations.