Gross ammonification, gross nitrification and N net mineralization in temperate forest soils at low temperatures

低温条件下氮素周转的温度依赖性尚不清楚。过去，温带森林土壤在冬眠季节低温下的氮矿化通常被认为可以忽略不计，但最近的研究结果对这一观点提出了质疑。在这里，我们将研究山毛榉和云杉林生态系统全年的原位氮净矿化率，以量化年尺度上冬季过程的相关性。在持续低温（+8,+5,+2,-1,-4°C）下的未扰动土壤样品的实验室实验中，我们将使用15N稀释技术研究两个地点不同土壤层的总氨化，总硝化和固定化的温度依赖性。为了验证底物的数量和质量影响这些过程的温度依赖性的假设，将添加不同的底物（总硝化时为NH4，总氨化时为甘氨酸、脯氨酸和2,6-吡啶二甲酸）。温度依赖性将用阿伦尼乌斯方程来量化。该项目的结果将在预测未来气候变化对森林土壤氮循环的影响时具有特殊的相关性。

The temperature dependency of N turnover at low soil temperatures is poorly known. In the past, N mineralization in temperate forest soils at low soil temperatures in the dormant season was often considered negligible, which is questioned by recent findings. Here, we will study rates of in situ N net mineralization throughout a full year in a beech and a spruce forest ecosystem to quantify the relevance of winterly processes at the annual scale. In laboratory experiments with undisturbed soil samples at constantly low temperatures (+8, +5, +2, -1, -4 °C) we will investigate the temperature dependency of gross ammonification, gross nitrification and immobilization in different soil horizons from both sites using the 15N dilution technique. To test the hypothesis that substrate quantity and quality influence the temperature dependency of these processes, different substrates (NH4 in case of gross nitrification; glycine, proline and 2,6-pyridindicarbonic acid in case of gross ammonification) will be added. Temperature dependencies will be quantified using the Arrhenius equation. The results of this project will be of special relevance when predicting effects of future climate change on the N cycle in forest soils.