Soil P availability along a catena located at the Sierra de Gata Mountains, Western Central Spain

The main objective of this study was to know the soil P availability in Quercus pyrenaica (deciduous oak) forests at the “Sierra de Gata” Mountains (Central Western Spain) and determine the factors controlling the availability of P in these soils. Twelve different oak stands along a rainfall gradient were selected, differentiating underlying geological materials: granites and schist-greywackes. Samples from selected soil horizons were taken and the available soil P was determined using an anion exchange membrane (PAEM). P retention capacity (PRC) was used as a rapid measure of soil P adsorption. P mineralization rate and acid phosphatase activity (APA) were determined in samples of the epipedons. Sites developed over schist-greywacke materials showed significantly lower contents of PAEM than sites over granites. Soil PRC was related positively to the contents of organically complexed Al + Fe and negatively to PAEM contents, confirming that metal–organic complexes play an important role in the solubility and availability of soil P. The APA did not show any direct relationship neither with the net P mineralization rate nor with PAEM, but did with the soil organic carbon (SOC) content. P mineralization did not only depend on the biochemical mineralization, but also on the biological mineralization of SOC by heterotrophic micro-organisms, which activity is favoured by the SOC content.