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

Abstract

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. 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. 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. 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.