C:P stoichiometric imbalance between soil and microorganisms drives microbial phosphorus turnover in the rhizosphere

The carbon-to-phosphorus (C:P) ratios of microorganisms were quantified in the rhizosphere and bulk soil collected from six typical fertilization regimes across three long-term experiments in humid (wheat–maize rotation), semiarid (wheat–maize rotation), and arid (maize–wheat–cotton rotation) climate zones. A 32P labeling incubation experiment allowed to test the relationship between microbial biomass P (MBP) turnover time and the C:P stoichiometric imbalance (SoilC:P/MicrobC:P) between soil (dissolved organic carbon:Olsen-P) and microorganisms (MBC:MBP). The MBC and MBN in the rhizosphere were 1.2 and 1.3 times higher than those in bulk soils, respectively, while the MBP was similar. The MBC:MBP ratio in the rhizosphere was 1.1 times higher than that in bulk soil, while the MBC:MBN ratio was similar. This finding suggested that C and P accumulation in the rhizosphere microorganisms was decoupled from that in the bulk soil. Compared to that in bulk soil, the MBP turnover in the rhizosphere was 1.1 times faster and microbially mediated P release was increased by 13% because of the decrease in the SoilC:P/MicrobC:P. Shoot P content was correlated with the rhizosphere SoilC:P/MicrobC:P and P flux mediated by microorganisms. The SoilC:P/MicrobC:P thresholds allowed to predict the start of an intensive competition between plants and microorganisms for P. Concluding, the stronger the SoilC:P/MicrobC:P in the rhizosphere decrease, the faster is the MBP turnover of homeostatic microorganisms, and furthermore, the microbially mediated P release leads to the decoupling of microbial biomass C and P at the root–soil interface. SoilC:P/MicrobC:P may be a predictor of the competition between plants and microorganisms. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.