Spatial Patterns of Phosphorus Fractions in Soils of Temperate Forest Ecosystems with Silicate Parent Material

Abstract. The stage of pedogenesis is a crucial indicator describing phosphorus (P) distribution, but also governing spatial P distribution patterns. Here, we assessed spatial patterns of P fractions and major P binding partners (e.g. organic C, pedogenic Fe and Al minerals) in a geosequence to describe spatial and pedogenetic changes of P distribution and to identify mechanisms for these changes. We found, that the distribution of total P was generally best matched by the distribution pattern of organic P, both showing decreasing content from the top- to the subsoil. Inorganic P was mainly ascribed as bound in unweathered rock at all sites, but with decreasing importance in later stages of pedogenesis. The pedogenetically young soil at Bad Brückenau also showed adsorbed inorganic P in the topsoil, probably due to high mineralization of organic P. Soil organic matter (SOM)-sesquioxide-complexes, as well as Al and Fe oxyhydroxides were identified as main binding partners of organic P at all stages of pedogenesis. With depth, the correlations of various P fractions with SOM decreased, whereas those with pedogenic Fe and Al oxyhydroxides increased. The change of sorbent is due to the mobilization of first Al, and in later stages of pedogenesis, of Fe in the topsoil. Both metals and its oxyhydroxides (Al(OH)i, Fe(OH)i) probably formed strong complexes with SOM and therefore retained P in the pedon. Due to the heterogeneous P distribution, our results suggest a differing ecosystem P nutrition strategy at each of our sites: from acquiring inorganic P from weathered primary rock to minimizing loss of organic P by recycling. We argue that even in early stages of pedogenesis, P recycling is a major driver of ecosystem P nutrition, however not as important as in later stages. We conclude that the stage of pedogenesis in silicate soils, as e.g. visible in degree and state of podzolization, serves as predictor for plant and microbial P nutritional strategies.