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

- Warm-season grazing did not affect Rs and its components.
- Cold-season grazing stimulated Rs, and increased Ra more than Rh.
- Grazing affected Rs more in dry and cold years than in wet and warm years.

As a traditional practice in grasslands, grazing significantly affects soil respiration (Rs). To improve our understanding of grassland carbon cycling, it is critical to partition the responses of soil respiration to grazing into autotrophic (Ra) and heterotrophic (Rh) respiration. In addition, it remains unclear how grazing patterns, such as warm- and cold- season grazing, influence Rs 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 Rs 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 Rs while cold-season grazing significantly increased Rs 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 Ra or Rh, whereas cold-season grazing enhanced Ra (23.2%) more than Rh (4.9%). Cold-season grazing affected Rs and Ra 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 Rs components to grazing, and suggests that different grazing patterns should be considered when evaluating future carbon cycles in grazing ecosystems on the Tibetan Plateau.