Soil microbial responses to altered environmental conditions: Understanding both patterns and mechanisms toward developing a predictive framework

Background/Question/Methods

How microbial communities will respond to climate change, and what role they will play in ecosystem responses, remain a source of great uncertainty. This uncertainty stems partly from a lack of understanding of the relative importance of microbial response mechanisms, including rapid physiological acclimation, community composition, dispersal from regional communities, and local adaptation. We also lack a broad scale picture of the primary drivers of microbial responses; for example, are microbial communities directly tracking climate or tracking plant community responses to climate? The development of a robust predictive framework will likely require the integration of both the ecological and evolutionary mechanisms underlying microbial responses together with the drivers of those responses. To that end, we studied how soil microbial communities were affected by precipitation at multiple scales, and asked whether rainfall was a primary driver of the observed responses. We used a combination of meta-analysis with published data from rainfall manipulations, field surveys along a steep local rainfall gradient, and lab incubation experiments.

Results/Conclusions

Across sites with large-scale rainfall manipulations, decreased rainfall treatments resulted in soil microbial responses that were substantially less predictable and more decoupled from plant responses than treatments where rainfall was increased relative to historical levels. Microbial and plant responses also became less coupled as precipitation was further increased as a proportion of the historical average. Based on four years of local field surveys, soil microbial communities responded strongly and predictably to soil moisture across a rainfall gradient, independent of plant community responses. In experimental manipulations, functional responses to altered soil moisture were constrained by historical moisture conditions. Overall, these findings are consistent with direct responses of soil microbial communities to rainfall and some degree of local adaptation to historical rainfall patterns. In addition, the extent of departure from historical climate conditions may determine the predictability of species responses to novel climates. Placing the ecological and evolutionary dynamics of microbial communities in the context of historical and future environmental variation may thus provide us with a framework for testing responses to future climate change.