Response of soil microbial -diversity to grazing in grassland ecosystems: A meta-analysis

Grazing is one of the most important forms of terrestrial use, and the soil microbial community plays an important role in nutrient cycling and biodiversity maintenance of grazing grassland, but the response of soil bacterial and fungal communities alpha-diversity to grazing and the potential mechanisms of grazing-induced soil microbial change have not been well synthesized. We conducted a meta-analysis of 87 pairs of globally distributed observations from 35 published papers to investigate the response of the soil microbial community to grazing and the underlying mechanisms. Our results showed that light grazing increased the soil bacterial community Shannon index by 2.4%, but the soil fungal Shannon index decreased by 21.4%. Yak (Bos grunniens) grazing significantly increased the soil bacterial and fungal Shannon index by 1.5% and 11.3%, respectively. Grazing duration of 5-10 years increased the soil bacterial Chao1 index by 9.1% and fungal Chao1 and evenness indexes by 11.3% and 30.4%, respectively. In areas with <400 mm of precipitation, grazing decreased the soil bacterial Simpson index, and in areas of >= 400 mm, grazing also reduced the soil bacterial Simpson and increased the fungal richness and evenness. A linear analysis between soil microbial alpha-diversity indexes and other related variables showed that soil bacterial and fungal communities alpha-diversity and abundance under grazing conditions were significantly and positively correlated with grassland vegetation, soil pH, soil water content (SWC), total nitrogen (TN), total phosphorus (TP), organic carbon (SOC), and nitrate nitrogen (NO3--N), suggesting that changes in microbial communities were the combined result of grazing-induced vegetation and soil changes. Our results revealed the effects of grazing on soil bacterial and fungal alpha-diversity and their underlying mechanisms, which provide a basis for advocating moderate grazing and studying grassland management practices.