Redfield-like Stoichiometry of Microbial Biomass in Terrestrial Ecosystems

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Redfield stoichiometry predicts that ratios of essential elements (i.e. carbon-C, nitrogen-N and phosphorus-P) are remarkably constant among marine organisms and closely reflect the prevailing ratios of elements in seawater. How soil microbes reflect the large variations of concentrations of these elements in soils has not been well investigated. We took advantage of a recently compiled database of global C, N, P, and sulfur-S concentrations in soils and microbes, and developed the relationships between them using a power function model. The C:N:P:S was estimated to be 287:17:1:0.8 for soils, and 42:6:1:0.4 for microbes. We found a convergence of the relationships between elements in soils and in soil microbial biomass across C, N, P, and S. The element concentrations in soil microbial biomass follow a homeostatic regulation curve with soil element concentrations, inferring a unifying mechanism of microbial assimilation of soil elements across C, N, P and S. This correlation explains the well-constrained yet slightly larger variation in C:N:P:S stoichiometry in soils than in microbial biomass. This finding provides a mathematical explanation of element imbalance in soils and soil microbial biomass, and offers fundamental insights for incorporating microbial contribution to nutrient cycling into Earth system models.

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