Ecotypes shape extracellular enzyme stoichiometries via microbial resource allocation

Abstract

Microorganisms allocate resources toward extracellular enzyme production in order to acquire limiting nutrients from complex organic matter. However, it remains unclear whether exoenzymatic stoichiometries (e.g., ratios between carbon-, nitrogen-, and/or phosphorus-acquiring enzymes) vary between natural and managed ecosystems. Accordingly, we assessed relationships between microbial community composition, exoenzymatic stoichiometries, and life history strategies (e.g., copiotrophs versus oligotrophs) in old growth forest and cropland soils. We found that cropland soils were associated with more abundant copiotrophic taxa, lignin degradation, and higher activities of nitrogen-acquiring and oxidative enzymes, while forest soils were associated with more abundant oligotrophic taxa, cellulose turnover, and larger microbial biomass pools. Two keystone taxa, Basidiomycota and Alphaproteobacteria, played strong roles in regulating exoenzymatic stoichiometries across both ecosystems. Notably, co-occurrence network analysis suggested relationships between exoenzymatic stoichiometries and microbial life-history strategies were stronger in disturbed cropland soils than old growth forest soils. Based on these results, we suggest increasing the quantity and diversity of organic matter inputs to cropland soils, while protecting forest soils through adaptive management practices, could enhance carbon flows through the microbial loop and promote soil organic carbon sequestration. Incorporating exoenzymatic stoichiometries into trait-based frameworks could further improve our ability to predict how changes in microbial community structure scale up to influence ecosystem function.