Minor Effects of Warming on Soil Microbial Diversity, Richness and Community Structure.

Climate warming has caused widespread global concern. However, how warming affects soil microbial diversity, richness, and community structure on a global scale remains poorly understood. Here we conduct a meta-analysis of 945 observations from 100 publications by collecting relevant data. The results show that field warming experiments significantly modify soil temperature (+1.8°C), soil water content (-3.2%), and soil pH (-0.04). However, field warming does not significantly alter the diversity, richness, and community structure of soil bacteria and fungi. Warming-induced changes in soil variables (i.e., ΔSoil water content, ΔpH), ΔTemperature and experimental duration are important factors influencing the microbial responses to warming. In addition, soil bacterial α-diversity (Shannon index) decreases significantly (-3.4%) when the warming duration is 3-6 years, and bacterial β-diversity increases significantly (35.2%) when warming exceeds 6 years. Meta-regression analysis reveals a positive correlation between the change of bacterial Shannon index and ΔpH. Moreover, warming produces more pronounced effects on fungal Shannon index and β-diversity in experimental sites with moderate mean annual temperature (MAT, 0°C-10°C) than in higher (> 10°C) or lower (< 0°C) MAT. Overall, this study provides a global perspective on the response of soil microorganisms to climate warming and improves our knowledge of the factors influencing the response of soil microorganisms to warming.