Yak (Bos grunniens) excreta further facilitate the positive effects of soil fauna on litter decomposition in alpine meadow ecosystems

The influence of grazing activity, specifically excreta deposition, on the positive contributions of soil fauna to litter decomposition was not comprehensively examined. We conducted a 660-day field experiment to test the interactive effects of yak excreta and soil fauna on litter decomposition and underlying driving mechanisms. We found adding yak excreta further increased the positive effect of soil fauna on litter decomposition. The strengths, and mechanisms of this promoting effects varied depending on excreta type and decomposition stage. The changes in litter decomposition constants increased by 116.3% and 98.2% with dung addition alone and both dung and urine addition, respectively. The time required to achieve 75% mass loss was the shortest (129% in advance) under the conditions of interaction between yak excreta and soil fauna. Importantly, our findings suggested that yak excreta regulate the role of soil fauna in litter decomposition through nutrient deposition of excreta, physical breakdown by soil fauna, and trophic interaction. In the early decomposition stage, the primary determinants included soil nitrogen and soil moisture. Conversely, during the later decomposition stage, soil carbon and soil pH became the pivotal factors. This study improves our knowledge of how grazing and soil fauna affect nutrient cycling in grasslands ecosystems.