We conducted a 15N tracer experiment in laboratory microcosms with field-fresh soil samples from a biodiversity experiment to evaluate the relationship between grassland biodiversity and N cycling. To embrace the complexity of the N cycle, we determined N exchange between five soil N pools (labile and recalcitrant organic N, dissolved NH4+ and NO3− in soil solution, and exchangeable NH4+) and eight N transformations (gross N mineralization from labile and recalcitrant organic N, NH4+ immobilization into labile and recalcitrant organic N, autotrophic nitrification, heterotrophic nitrification, NO3− immobilization, adsorption of NH4+) expected in aerobic soils with the help of the N-cycle model Ntrace. We used grassland soil of the Jena Experiment, which includes plant mixtures with 1 to 60 species and 1 to 4 functional groups (legumes, grasses, tall herbs, small herbs). The 19 soil samples of one block of the Jena Experiment were labeled with either 15NH4+ or 15NO3- or both. In the presence of legumes, gross N mineralization and autotrophic nitrification increased significantly because of higher soil N concentrations in legume-containing plots and high microbial activity. Similarly, the presence of grasses significantly increased the soil NH4+ pool, gross N mineralization, and NH4+ immobilization, likely because of enhanced microbial biomass and activity by providing large amounts of rhizodeposits through their dense root systems. In our experiment, previously reported plant species richness effects on the N cycle, observed in a larger-scale field experiment within the Jena Experiment, were not seen. However, specific plant functional groups had a significant positive impact on the N cycling in the incubated soil samples.

中文翻译：

---

生物多样性 - 氮循环关系：对来自不同多样性植物混合物的土壤进行 15N 示踪实验，以模拟氮库大小和转化率

我们在实验室微观世界中进行了 15N 示踪剂实验，使用来自生物多样性实验的田间新鲜土壤样本来评估草地生物多样性与氮循环之间的关系。为了适应 N 循环的复杂性，我们确定了五个土壤 N 库（不稳定和顽固的有机 N、土壤溶液中溶解的 NH4+ 和 NO3−，以及可交换的 NH4+）和八个 N 转化（来自不稳定和顽固的总 N 矿化）之间的 N 交换有机氮、NH4+ 固定为不稳定和顽固的有机氮、自养硝化作用、异养硝化作用、NO3− 固定化、NH4+ 的吸附）在好氧土壤中预期在 N 循环模型 Ntrace 的帮助下。我们使用了耶拿实验的草地土壤，其中包括具有 1 到 60 个物种和 1 到 4 个功能组（豆类、草、高草，小草）。耶拿实验的一个街区的 19 个土壤样品用 15NH4+ 或 15NO3- 或两者标记。在豆类存在的情况下，由于含豆类地块土壤氮浓度较高，微生物活性高，总氮矿化和自养硝化作用显着增加。类似地，草的存在显着增加了土壤 NH4+ 池、总氮矿化和 NH4+ 固定化，这可能是因为通过其密集的根系提供大量根系沉积物来增强微生物生物量和活性。在我们的实验中，之前报道的植物物种丰富度对氮循环的影响，在耶拿实验中的大规模田间实验中观察到的，没有看到。然而，