Soil bacterial community responses to warming and grazing in a Tibetan alpine meadow.

Warming and grazing significantly affect the structure and function of an alpine meadow ecosystem. Yet, the responses of soil microbes to these disturbances are not well understood. Controlled asymmetrical warming (+1.2/1.7°C during daytime/nighttime) with grazing experiments were conducted to study microbial response to warming, grazing and their interactions. Significant interactive effects of warming and grazing were observed on soil bacterial α-diversity and composition. Warming only caused significant increase in bacterial α-diversity under no-grazing conditions. Grazing induced no substantial differences in bacterial α-diversity and composition irrespective of warming. Warming, regardless of grazing, caused a significant increase in soil bacterial community similarity across space, but grazing only induced significant increases under no-warming conditions. The positive effects of warming on bacterial α-diversity and grazing on community similarity were weakened by grazing and warming, respectively. Soil and plant variables explained well the variations in microbial communities, indicating that changes in soil and plant properties may primarily regulate soil microbial responses to warming in this alpine meadow. The results suggest that bacterial communities may become more similar across space in a future, warmed climate and moderate grazing may potentially offset, at least partially, the effects of global warming on the soil microbial diversity.