Differential effects of grazing, water, and nitrogen addition on soil respiration and its components in a meadow steppe

Background and aims Understanding the influences of environmental variation and anthropogenic disturbance on soil respiration (R-S) is critical for accurate prediction of ecosystem C uptake and release. However, surprisingly, little is known about how soil respiration and its components respond to grazing in the context of global climate change (i.e., precipitation or nitrogen deposition increase). Methods We conducted a field manipulative grazing experiment with water and nitrogen addition treatments in a meadow grassland on the Songnen Plain, China, and assessed the combined influences of grazing and global change factors on R-S, autotrophic respiration (R-A), and heterotrophic respiration (R-H). Results Compared with the control plots, R-S, R-A and R-H all exhibited positive responses to water or nitrogen addition in the wet year, while a similar effect occurred only for R-H in the dry year. The responses of R-S to precipitation regimes were dominated by both frequency and amount. However, grazing significantly inhibited both soil respiration and its components in all subplots. Further analysis demonstrated that the plant root/shoot ratio, belowground biomass and microbial biomass played dominant roles in shaping these C exchange processes. Conclusion These findings suggest that changes in precipitation regimes, nitrogen deposition, and land utilization may significantly alter soil respiration and its component processes by affecting local carbon users (roots and soil microorganism) and carbon substrate supply in meadow steppe grasslands. The future soil carbon sequestration in the studied meadow steppe will be benefited more by the moderate grazing disturbance.