Physiological and predicted metagenomic analysis of soil aggregate microbial communities under different tillage regimes

Soils are spatially heterogeneous environments, and the distribution of microorganisms and carbon is organized at the scale of millimeters in soil aggregates. The physio-chemical environment within macroaggregates and microaggregates differ, which may lead to the selection of microbial communities with different survival and growth strategies- here termed life history strategies. Using an aggregate scale survey of microbial communities in agricultural soils, I show that soil aggregates harbor distinct communities with life history characteristics that align with the Yield, Acquisition, Stress tolerator framework (Y-A-S). Soils collected from an eight- year tillage experiment were isolated into four aggregate size classes and physiological measurements of enzyme activity, multiple substrate induced respiration, and carbon use efficiency were conducted to reveal tradeoffs in community resource allocation. Carbon and nitrogen acquiring enzyme activity was highest in macroaggregates \u3e2mm and this was negatively correlated with carbon use efficiency, which is consistent with an Acquisition- Yield strategy tradeoff. Carbon use efficiency was highest in microaggregate communities. Substrate induced respiration revealed that aggregate microbial communities showed patterns of carbon substrate preference across aggregate size class; however, these patterns were not consistent with the Y-A-S framework. Community stress tolerance was assessed using predictive metagenomics which revealed an enrichment in genes consistent with a Stress tolerator strategy in microaggregates \u3c0.25mm. Together, these findings show that understanding the role of the soil physical environment in shaping microbial life histories may help us to predict how agricultural management affects the fate of carbon in soils