Redundancy of microbial P mobilization in beech forest soils with contrasting P stock: A microbial dilution experiment

Phosphorus (P) acquisition in forest ecosystems relies on litter cycling, but foliar P concentrations in beech forests are decreasing. This highlights the urgency to understand how soil microbes adapt to P limitations caused by environmental shifts. In this study, a novel approach combining 33 P-wick labeling to trace litter-P recycling with a microbial dilution approach was used to study microbial P cycling associated with microbial biodiversity loss. Sterilized soils, re-inoculated with different dilutions of their native microbial communities were incubated with 33 P-labeled beech litter for four weeks. The kinetics of acid phosphatase and the flux of 33 P into different soil pools were determined. Carbon (C), nitrogen (N), and P, in soil microbial biomass and in extractable pools (e.g., P resin ) were measured. The acid phosphatase activity decreased by 75–92 % with the dilution increase from 10 −4 to 10 −6 at the P-rich site, indicating a functional loss of P mobilization. The overall acid phosphatase activity was 1-fold higher at the P-deficient site than at the P-rich site, suggesting a high functional redundancy of microbial P mobilization. The recoveries of litter-derived 33 P in soil microbial biomass (SMB) and in P resin were 5-fold and 2-fold higher for the P-deficient site than for the P-rich site throughout all dilutions, suggesting that the recycling of litter-P by SMB in the P-deficient soil is highly redundant as an intermediate reservoir. Our study confirms that the high functional redundancy of microbial P acquisition at a P-deficient forest site can maintain pivotal microbial acquisition processes for P uptake. • Microbial diversity loss alters microbial P mobilization in the P-rich soil. • Microbial P immobilization is functionally redundant in the P-deficient soil. • Litter-P plays a crucial role in microbial P cycling in the P-deficient soil. • The functional redundancy of P acquisition relates to homeostatic microbial C:N:P.