Responses of soil respiration to soil management changes in an agropastoral ecotone in Inner Mongolia, China

Studying the responses of soil respiration (Rs) to soil management changes is critical for enhancing our understanding of the global carbon cycle and has practical implications for grassland management. Therefore, the objectives of this study were (1) quantify daily and seasonal patterns of Rs, (2) evaluate the influence of abiotic factors on Rs, and (3) detect the effects of soil management changes on Rs. We hypothesized that (1) most of daily and seasonal variation in Rs could be explained by soil temperature (Ts) and soil water content (Sw), (2) soil management changes could significantly affect Rs, and (3) soil management changes affected Rs via the significant change in abiotic and biotic factors. In situ Rs values were monitored in an agropastoral ecotone in Inner Mongolia, China, during the growing seasons in 2009 (August to October) and 2010 (May to October). The soil management changes sequences included free grazing grassland (FG), cropland (CL), grazing enclosure grassland (GE), and abandoned cultivated grassland (AC). During the growing season in 2010, cumulative Rs for FG, CL, GE, and AC averaged 265.97, 344.74, 236.70, and 226.42 gC m-2 year-1, respectively. The Ts and Sw significantly influenced Rs and explained 66%-86% of the variability in daily Rs. Monthly mean temperature and precipitation explained 78%-96% of the variability in monthly Rs. The results clearly showed that Rs was increased by 29% with the conversion of FG to CL and decreased by 35% and 11% with the conversion of CL to AC and FG to GE. The factors impacting the change in Rs under different soil management changes sequences varied. Our results confirm the tested hypotheses. The increase in Q10 and litter biomass induced by conversion of FG to GE could lead to increased Rs if the climate warming. We suggest that after proper natural restoration period, grasslands should be utilized properly to decrease Rs.