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

在低土壤温度下氮周转的温度依赖性知之甚少。在过去，温带森林土壤中的氮矿化在休眠季节的低土壤温度往往被认为是微不足道的，这是最近的研究结果提出质疑。在这里，我们将研究原位氮净矿化率在全年的山毛榉和云杉林生态系统，以量化的相关性，在年度尺度上的冬季过程。在持续低温（+8、+5、+2、-1、-4 °C）下对原状土壤样品进行的实验室实验中，我们将使用15 N稀释技术研究两个地点不同土层中总氨化作用、总硝化作用和固定作用的温度依赖性。为了检验底物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（在总硝化的情况下为NH 4;在总氨化的情况下为甘氨酸、脯氨酸和2，6-吡啶二甲酸）。将使用Arrhenius方程量化温度依赖性。该项目的结果将是特别相关的预测未来气候变化对森林土壤中的氮循环的影响。

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.