Characterizing changes in soil bacterial community structure in response to short-term warming

High altitude alpine meadows are experiencing considerably greater than average increases in soil surface temperature, potentially as a result of ongoing climate change. The stimulatory effects of warming on plant productivity and soil edaphic variables have been established previously, but the influence of warming on soil microbial community diversity and structure has not been well characterized, especially in climate sensitive regions. Here, the impact of 16 months of soil warming (both +1 and +2 °C) on microbial community structure was examined in a field experiment on a Tibetan Plateau alpine meadow using 16S rRNA amplicon sequencing. Warming dramatically altered the beta diversity of the soil bacterial community, but the alpha diversity was not significantly affected. Overall, warming significantly decreased the abundance of Acidobacteria and Bacteroidetes, while Actinobacteria significantly increased. Changes in the abundance of the Actinobacteria and Alphaproteobacteria were found to contribute the most to differences between ambient and warmed conditions. Additionally, a significant (p = 0.037) increase in the Alphaproteobacteria to Acidobacteria ratio was observed, which may contribute to increased soil respiration. Mantel tests indicate that the variation in bacterial community structure is closely correlated with soil edaphic and plant phenotypic properties. Interestingly, certain taxa showed a non-linear response to the two warming treatments, for example, Deltaproteobacteria showed a decreased relative abundance at +1 °C, but a return to ambient control relative abundance at +2 °C. This suggests complex microbial dynamics that could result from conditional dependencies between bacterial taxa.