Impacts of N/P inputs on organic P dynamics and P status in soils and plants along a nutrient gradient

Our aim within the SPP 1685 is to investigate to which extent the effect of mineral N and P inputs on soil biological processes is reflected in nutrient uptake by beech trees. We hypothesize that because of the effect of mineral fertilizer on the distribution of inorganic and organic P species in soil (see project of Frossard/Tamburini), the source for tree P and N nutrition will be shifted. This shift will be most pronounced in Lüss where tree nutrition based on mineralization of organic P likely will be replaced by uptake from mineral sources (shift from recycling to acquiring ecosystem).

We will rely on 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). We plan to extend the set of field sites because of the unique opportunity to study the fate of fertilizer-P by radioactive isotopes under field conditions in a forest at the FZ Jülich (intermediate in terms of soil P fractions as compared to Lüss and Bad Brückenau). We will use stable and radioactive isotope techniques. Using these complementary tools we will be able to quantify plant P pools, and fluxes of P between pools in soils and plants, and identify the contribution of different sources for plant nutrition.