Interactive effects of grazing and global change factors on soil and ecosystem respiration in grassland ecosystems: A global synthesis

As the key carbon (C) fluxes between biosphere and atmosphere, soil respiration (R_s) and ecosystem respiration (R_e) play vital roles in regulating global C balance and climate-biosphere feedback in the Earth system. Despite the fact that numerous manipulative studies and a few meta-analyses have been conducted to examine the responses of R_s and its components (i.e. autotrophic [R_a] and heterotrophic respiration [R_h]) as well as R_e to grazing (G) or global change factors, the interactive effects between grazing and global change factors remain poorly understood. Here, we performed a comprehensive meta-analysis of manipulative experiments with both grazing and global change factors to quantify their individual and interactive effects on R_s and its components as well as R_e. Our results showed that grazing and drought significantly decreased R_s by 12.35% and 20.95%, respectively, whereas warming (W), nitrogen addition (N) and increased precipitation (P) stimulated it by 2.12%, 5.49% and 13.44%, respectively. Similarly, grazing, warming, nitrogen addition and increased precipitation increased R_e by 7.21%, 4.94%, 48.45% and 21.57%, respectively, while drought decreased it by 16.86%. However, the combinations of grazing with warming (GW), nitrogen addition (GN) and increased precipitation (GP) exhibited non-significant effects on R_s. More importantly, additive interactions between grazing and global change factors exhibited a substantial predominance on R_s, R_a, R_h and R_e rather than synergistic and antagonistic ones. Synthesis and applications. Our findings highlight the crucial importance of the interactive effects between grazing and global change factors on soil respiration (R_s) and ecosystem respiration (R_e). Therefore, incorporating this key influence on ecosystem processes into Earth system models (ESMs) could better improve the prediction of climate-biosphere feedbacks and develop sustainable strategies for grassland management in the Anthropocene.