Nitrogen and Phosphorus Cycling

植物多样性对草地土壤养分循环的反馈，例如通过有机质输入和适应的微生物群落，可能发生在建立初期之后。在耶拿试验中，在高度多样化的混合物下增加土壤中的C和N储量，导致5年后植物多样性与土壤中植物有效化学N物种浓度之间的负相关转变为正相关。同时，土壤中的磷库减少。到目前为止，还不存在生物多样性发展与土壤营养库关系的长期观测。我们建议阐明土壤中N的积累和释放随时间的增加与植物多样性有关的潜在过程，即气态N沉积、植物对地下水的吸收和总N的矿化，并继续监测生物多样性-N和P的循环关系。我们将用15NO2标记实验测定SOM中NO2来源的N，用同位素标记SeO42-测定植物对地下水中NO3-的吸收，用15N池稀释法测定就地总矿化。我们将在主要实验的所有地块使用已建立的集雨器和吸盘，继续我们8年的地上和地下水和养分通量的数据集。我们主要参与了拟议研究单元的示踪实验(6.2)和主要实验(6.3)，但也为另外两个实验(6.1、6.4)提供了可用的N和P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).