|Brucker, E; Kernchen, S; Spohn, M: Release of phosphorus and silicon from minerals by soil microorganisms depends on the availability of organic carbon, Soil Biology and Biochemistry, 143(107737) (2020), doi:10.1016/j.soilbio.2020.107737|
Microorganisms release nutrients from minerals. However, this process is not yet well understood despite its importance for soil fertility. The aim of this study was to determine which factors control microbial phosphorus (P) and silicon (Si) release from apatite and weathered rock, and to analyze which microbial-mediated processes cause P and Si solubilization. For this purpose, we conducted a series of incubation experiments with apatite and saprolite (weathered bedrock) and soil extracts of four soils that are located along a climate gradient in the Coastal Cordillera of Chile and differ in soil P fractions and degree of weathering. We developed an approach that allowed us to measure the release of P from apatite and the release of Si from saprolite by microbial consortia in soil solution. The microbial consortia of all soil extracts caused release of P from apatite. The addition of carbon (C) and nitrogen (N) to the soil solution increased the rate of microbial P solubilization from apatite by a factor of about 10 in all soil depth increments. The pH decreased strongly during the incubations. In the depth increments 0.1–0.2 and 0.4–0.6 m, the P solubilization rates were negatively correlated with the pH measured at the end of the incubation (r2 ¼ 0.55 and 0.76, respectively, both p < 0.01). Nine organic acids were detected throughout the experiment. The total concentration of carboxyl groups was positively correlated with the P solubilization rate (r2 ¼ 0.94, p < 0.01). The addition of dissolved inorganic P to the soil extracts did not significantly decrease the P solubilization rates. The rate of microbial Si solubilization from saprolite increased strongly with the surface area of the saprolite. We conclude that microbial solubilization of P from apatite was limited by the availability of easily decomposable C and that microbial solubilization of P from apatite was not affected by P availability, indicating that this process is not or not exclusively controlled by microbial need for P. In conclusion, our results indicate that microbial weathering of minerals in saprolite is strongly constrained by the availability of organic C and by the specific surface area of the saprolite.