Impacts of N and P inputs on organic P dynamics and P status in temperate forest soils

The main goal of our contribution within the SPP 1685 is to investigate to which extent soil biological processes in the soil organic layer are affected by mineral N and P inputs. We will use molecular microbiological tools and 31P nuclear magnetic resonance (NMR) analysis together with stable and radioactive isotope techniques. We will mainly investigate the NxP fertilization experiment at the two contrasting beech forest field sites Bad-Brückenau (high amount of available P) and Lüss (little amount of available P). On an additional beech forest site in Jülich, a similar short fertilization experiment will be set up to enable the use of P radioisotopes.
We will analyze bacterial, fungal and the phosphatase gene harboring microbial communities. This will provide information on how the bacterial and fungal community composition and function change after nutrient addition. Potential alkaline and acid phosphatase activities and efficiencies will be determined.
Soil P pools will be quantified by sequential chemical extractions. Stable isotopes and radioisotopes will allow us to quantify fluxes among these soil pools and investigate processes behind those fluxes. The isotopic composition of oxygen associated to P is an indicator for biological activity and will give us information whether a given phosphate molecule has been released from a mineral or an organic P compound. In addition, phosphorus radioisotopes will be used to trace the incorporation of P fertilizer into soil P pools. Further, NMR will be used to characterize the molecular nature of organic P under the different treatments.