How soil microbes assimilate carbon-C, nitrogen-N, phosphorus-P and sulfur-S is fundamental for understanding nutrient cycling in terrestrial ecosystems. We compiled a global database of C, N, P and S concentrations in soils and microbes and developed relationships between them by 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 across C, N, P and S, implying a unifying mechanism of microbial assimilating soil elements. This correlation explains the well-constrained C:N:P:S stoichiometry with a slightly larger variation in soils than in microbial biomass. Meanwhile, it is estimated that the minimum requirements of soil elements for soil microbes are 0.8 mmol C Kg−1 dry soil, 0.1 mmol N Kg−1 dry soil, 0.1 mmol P Kg−1 dry soil and 0.1 mmol S Kg−1 dry soil, respectively. These findings provide a mathematical explanation of element imbalance in soils and soil microbial biomass and offer insights for incorporating microbial contribution to nutrient cycling into Earth system models.
Xu, X., Hui, D., King, A. et al. Convergence of microbial assimilations of soil carbon, nitrogen, phosphorus and sulfur in terrestrial ecosystems. Sci Rep 5, 17445 (2015). https://doi.org/10.1038/srep17445