New insights into the patterns of ecoenzymatic stoichiometry in soil and sediment

Abstract

Ecoenzymatic stoichiometry connects the elemental stoichiometry of microbial biomass and detrital organic matter to microbial nutrient assimilation and growth, and thus has been proposed and developed to estimate microbial nutrient limitations. However, the theories and methods developed so far have not yet clearly explored the critical thresholds of ecoenzymatic stoichiometry that identify whether nutrient limitation occurs or not. Here, we developed methods quantifying critical thresholds for microbial carbon (C), nitrogen (N) and phosphorus (P) limitations by centering on the potential responses of microbial resource use efficiency to nutrient limitations. We also provided new insight into the relationships of bivariate regressions between C-, N- and P-acquiring ecoenzymatic activities by reconsidering the intercept of regressions as an index to initial nutrient limitations, and consequently distinguished six initial limitation scenarios based on the range of values for these intercepts. According to the empirical values of the regression intercepts, the overall frequency of primary nutrient limitations in microbial communities across a global suite of soils and sediments is P limitation > N limitation > C limitation. The result implies that P and N availabilities rather than that of C could be the most important limitations on microbial production and metabolism in terrestrial soils and freshwater sediments. Nutrient limitations in heterotrophic microbial communities are fundamental characteristics of both soil and sediment systems, which regulate organic matter decomposition and element cycles. Our perspective provides a foundational framework and avenue for understanding and quantifying microbial nutrient limitations in studies of terrestrial C cycling and microbial ecology.