Soil microbes become a major pool of biological phosphorus during the early stage of soil development with little evidence of competition for phosphorus with plants.

Aims: We aimed to quantify the pool size of soil microbial biomass P (Pmic) during the early stage of soil development up to 125 years after glacial retreat in the Gongga Mountains, China and relate the pool size of Pmic to the plant P (Pplant) pools in the ecosystem. Methods: We determined the pool sizes of P in soil microbes, plants and soils and the P fluxes with plant uptake and litterfall in successional ecosystems at five study sites along the 125-year Hailuogou glacial retreat chronosequence. Moreover, we estimated the flux of P cycled through microbial biomass (Pmic cycling) based on literature data. We also approached the likelihood of P competition between plants and soil microbes based on the P status of the plants, soils and soil microbes. Results: The size of the Pmic pools (0.2–8.3 g m−2) in the organic layer and top 10 cm of the mineral soils was comparable to that of the Pplant pools (0.3–9.1 g m−2) at all study sites along the Hailuogou chronosequence. Based on the literature, the Pmic cycling at our study site (0.3–13.5 g m−2 year−1 if estimated based on temporal fluctuations of Pmic, 5.2–268 g m−2 year−1 if estimated based on the isotope dilution method) was at least one order of magnitude larger than the Pplant uptake (not detected-0.36 g m−2 year−1) and the Pplant return by litterfall (not detected-0.16 g m−2 year−1). Although Pmic became a major pool of biological P, we did not find indications of P competition between plants and soil microbes as indicated by the positive relationships between the concentrations of Pmic and plant-available P in soils and the P-rich status of plants and soil microbes. Conclusions: Soil microbial biomass already becomes a major P pool in the early stage of soil development. Our estimations based on the literature suggest that Pmic cycling is probably the largest P flux in the studied up to 125-year ecosystems. Plants likely did not suffer P competition with microbes, in part due to the preferential decomposition of the P-rich compounds from dead microbial biomass which led to net P mineralization. [ABSTRACT FROM AUTHOR]