Soil bacterial community responses to altered precipitation and temperature regimes in an old field grassland are mediated by plants.

The structure and function of soil microbiomes often change in response to experimental climate manipulations, suggesting an important role in ecosystem feedbacks. However, it is difficult to know if microbes are responding directly to environmental changes or are more strongly impacted by plant responses. We investigated soil microbial responses to precipitation and temperature manipulations at the Boston-Area Climate Experiment in Massachusetts, USA, in both vegetated and bare plots to parse direct vs. plant-mediated responses to multi-factor climate change. We assessed the bacterial community in vegetated soils in 2009, two years after the experiment was initiated, and bacterial and fungal community in vegetated and bare soils in 2011. The bacterial community structure was significantly changed by the treatments in vegetated soils. However, such changes in the bacterial community across the treatments were absent in the 2011 bare soils. These results suggest that the bacterial communities in vegetated soils were structured via plant community shifts in response to the abiotic manipulations. Co-variation between bacterial community structure and temperature sensitivities and stoichiometry of potential enzyme activities in the 2011 vegetated soils suggested a link between bacterial community structure and ecosystem function. This study emphasizes the importance of plant-soil-microbial interactions in mediating responses to future climate change.