While soil microbial communities are well known drivers of soil carbon cycling, their sensitivity to climate change and thus their role in terrestrial ecosystem responses to climate change remain uncertain. The degree of local adaptation and responsiveness to change in the soil environment will partly determine the microbial contribution to soil carbon balance under altered climate conditions. We examined whether soil microbes were specialized to local climate and how they responded to altered precipitation regimes. We focused on soil fungi, both saprophytic and mycorrhizal, because they dominate most temperate soils, play significant roles in soil carbon cycling, and affect plant community diversity and productivity. Experimental sites were located in grasslands across a steep natural precipitation gradient (~90-40 cm mean annual rainfall across ~400 km) on the Edwards Plateau in central Texas with rocky limestone soils. We tracked soil fungi across the gradient over three years to examine annual variation in fungal responses to soil moisture availability. Additionally, we used reciprocal manipulations of soil moisture for soils across the gradient to elucidate the mechanisms of fungal responses to climate change.

Results/Conclusions

We found that fungal networks in soil rapidly responded to annual precipitation, while root networks were buffered against environmental change. Across the precipitation gradient, soil fungal networks declined linearly from wetter to drier sites and microbial exoenzyme production exhibited threshold responses to soil moisture. In experimental manipulations, functional responses to altered precipitation in terms of decomposition and enzyme production generally increased with more soil moisture regardless of soil origin. Response breadth, however, was narrower for soils from drier habitats, suggesting more limited microbial functional potential. These findings are consistent with moisture thresholds for soil function that may be important switch points for soil resistance and resilience to climate change. Understanding the generality of local microbial specialization and sensitivity to altered precipitation may help us to predict soil responses and feedbacks to future climate change.