Small-scale spatial distribution of phosphorus fractions in soils from silicate parent material with different degree of podzolization

The spatial heterogeneity of phosphorus (P) and different P forms in soils has implications for plant, microbial, and ecosystem P supply. Little information is available concerning the small-scale vertical and horizontal distributions of P and important variables for P binding at the soil profile scale. We assessed spatial patterns of total P and different P fractions, and of major P binding partners (e.g. soil organic matter: SOM, pedogenic Fe and Al minerals) with geostatistical methods in soil profiles and soil profile compartments formed from siliceous parent material and stocked with mature Fagus sylvatica forest to describe spatial and pedogenetic changes of P distribution and to address mechanisms for these changes. As expected, we found that the distribution of total P was generally best matched by the distribution pattern of organic P, both showing decreasing contents from the top- to the subsoil. Inorganic P was mainly ascribed as bound in primary silicate minerals at all sites, but with decreasing importance in later stages of podzolization. SOM, Al and Fe oxyhydroxides as well as SOM-Al/Fe oxyhydroxide complexes were identified as main binding partners of organic P at all sites. With increasing depth, correlations of various P fractions with SOM decreased, whereas those with pedogenic Fe and Al oxyhydroxides increased. This pattern is assigned to the mobilization of first pedogenic Al minerals, and in later stages of podzolization, also of pedogenic Fe minerals in the topsoil. Our results support the concept of different ecosystem P nutrition strategies at each of our sites: ranging from acquiring inorganic P from weathered parent material to minimizing loss of organic P by recycling. Assessing the small-scale soil variability enables investigating the influence of podzolization intensity in temperate forest soils on the spatial P distribution at the profile scale.