Warm- and cold- season grazing affect soil respiration differently in alpine grasslands

As a traditional practice in grasslands, grazing significantly affects soil respiration (R_s). To improve our understanding of grassland carbon cycling, it is critical to partition the responses of soil respiration to grazing into autotrophic (R_a) and heterotrophic (R_h) respiration. In addition, it remains unclear how grazing patterns, such as warm- and cold- season grazing, influence R_s and its components in alpine grasslands that are subject to increasing grazing pressure. Here, we conducted a six-year manipulative experiment combining with a meta-analysis, to investigate the responses of R_s and its components to moderate grazing in a Tibetan alpine grassland. Grazing patterns included warm-season grazing by sheep during the growing seasons of 2008 to 2010 and simulating cold-season grazing by clipping during the non-growing seasons of 2011 to 2013. Our results showed that warm-season grazing minimally affected R_s while cold-season grazing significantly increased R_s by 13.1%. This result was supported by a meta-analysis at seven grassland sites across the Tibetan Plateau. Further, we found that warm-season grazing did not affect R_a or R_h, whereas cold-season grazing enhanced R_a (23.2%) more than R_h (4.9%). Cold-season grazing affected R_s and R_a differently depending on interannual variation in climate conditions. A significant increase of 17.1% and 26.3%, respectively, was recorded in dry and cold years, but no change was recorded in wet and warm years. This study highlights the differential responses of R_s components to grazing, and suggests that different grazing patterns should be considered when evaluating future carbon cycles in grazing ecosystems on the Tibetan Plateau.