Nitrogen and Phosphorus Cycling

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Feedbacks of plant diversity on nutrient cycling in soil under grassland e.g., mediated through organic matter input and adapted microbial communities, might occur after an initial period of establishment. In the Jena Experiment, increased C and N storage in soil under highly diverse mixtures resulted in a shift from negative to positive correlations between plant diversity and concentrations of plant-available chemical N species in soil after five years. Simultaneously, the P pool in soil decreased. Up to now, no longer-term observations of the development of biodiversity-soil nutrient pool relationships exist. We propose to elucidate the underlying processes of accumulation and enhanced release of N in soil with time as related to plant diversity i.e., gaseous N deposition, uptake of groundwater by plants, and gross N mineralization, and to continue monitoring the biodiversity-N and P cycling relationships. We will determine NO2-derived N in SOM with a 15NO2-labeling experiment, plant uptake of NO3 - from groundwater with isotopically labeled SeO4 2-, and in-situ gross mineralization with the 15N pool dilution method. We will continue our 8-yr data set of above and belowground water and nutrient fluxes using established rain collectors and suction plates at all plots of the Main Experiment. We mainly contribute to the Tracer Experiment (6.2) and the Main Experiment (6.3) of the proposed research unit but also provide available N and P concentration data to two other experiments (6.1, 6.4).