Abstract. Efforts to understand and model the current and future behavior of the global
phosphorus (P) cycle are limited by the availability of global data on rates of soil P processes, as well as their environmental controls. Here, we present a novel isotope pool dilution approach using 33P labeling of live and sterile soils, which allows for high-quality data on gross fluxes of soil inorganic P (Pi) sorption and desorption, as well as of gross fluxes of organic P mineralization and microbial Pi uptake to be obtained. At the same time, net immobilization of 33Pi by soil microbes and abiotic
sorption can be easily derived and partitioned. Compared with other approaches, we used short incubation times (up to 48 h), avoiding tracer
remineralization, which was confirmed by the separation of organic P and Pi using isobutanol fractionation. This approach is also suitable for strongly weathered and P-impoverished soils, as the sensitivity is increased by the extraction of exchangeable bioavailable Pi (Olsen Pi; 0.5 M NaHCO3)
followed by Pi measurement using the malachite green assay. Biotic
processes were corrected for desorption/sorption processes using adequate
sterile abiotic controls that exhibited negligible microbial and
extracellular phosphatase activities. Gross rates were calculated using
analytical solutions of tracer kinetics, which also allowed for the study of gross
soil P dynamics under non-steady-state conditions. Finally, we present major
environmental controls of gross P-cycle processes that were measured for
three P-poor tropical forest and three P-rich temperate grassland soils.
Supplementary material to "A novel isotope pool dilution approach to quantify gross rates of key abiotic and biological processes in the soil phosphorus cycle"
