Nitrogen and Phosphorus Cycling

草地下植物多样性对土壤养分循环的反馈，如通过有机质输入和适应微生物群落介导，可能发生在初始建立期之后。在耶拿试验中，在高度多样化的混合条件下，土壤中C和N储量增加，导致植物多样性与土壤中植物有效态化学氮浓度在5年后由负相关转为正相关。同时，土壤磷库减少。到目前为止，还没有对生物多样性与土壤养分库关系的发展进行长期观察。我们建议阐明与植物多样性相关的氮在土壤中积累和释放的潜在过程，即气态氮沉积、植物对地下水的吸收和总氮矿化，并继续监测生物多样性-氮和磷循环关系。我们将通过15no2标记实验、同位素标记SeO4 2-的植物从地下水中吸收NO3 -和15N池稀释法的原位总矿化来测定SOM中的no2衍生N。我们将在主试验的所有地块使用已建立的雨水收集器和吸盘，继续我们8年的地上和地下水和养分通量数据集。我们主要对拟建研究单元的示踪实验（6.2）和主实验（6.3）做出贡献，但也为另外两个实验（6.1,6.4）提供可用的氮和磷浓度数据。

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).