Drought increases microbial allocation to stress tolerance but with few tradeoffs among community-level traits

Climate change will increase soil drying, altering microbial communities via increasing water stress and decreasing resource availability. The responses of these microbial communities to changing environments is likely governed by physiological tradeoffs between high yield, resource acquisition, and stress tolerance (Y-A-S framework). We leveraged a unique field experiment that manipulates both drought and carbon availability across two years and three land uses, and we used both metagenomic and bioassay indicators of the three microbial community traits to test the following hypotheses: 1. Drought increases microbial allocation to stress tolerance functions, at the expense of growth and resource acquisition. 2. Because microbes are resource-limited under drought, increased carbon will enable greater expression of stress tolerance. 3. All three key life history traits described in the YAS framework will trade off, especially when resources are limited. Drought did increase microbial physiological investment in stress tolerance (measured via trehalose production), but we saw few other changes in microbial communities under drought. Carbon addition increased resource acquisition (measured via enzyme activity and resource acquisition gene abundance) and stress tolerance (trehalose assay), but did so in both drought and average rainfall environments. We found no evidence of trait tradeoffs, as we found no significant negative correlations between traits (measured via bioassay and metagenomics). In summary, we found C addition, and to a lesser extent, drought, both altered microbial community function and functional genes. However, resources did not alter drought response in a way that was consistent with theory of life history tradeoffs.