Fluxes and mechanisms of permanent nitrogen removal and N2O production in a heavy nitrogen loaded regions of China

三角洲地区是农业集约化的重氮负荷区，过量的氮素会造成湖泊富营养化、藻类水华、温室效应、地下水污染等生态环境问题。中国研究小组最近的一项N预算研究表明，陆地生态系统永久失去了一半以上的N负荷，一氧化二氮(N2O)排放量随着N投入的增加呈指数增长。然而，由于测量各种基本过程的所有N产物的方法上的困难，尚不清楚这种永久性的N去除发生在何时何地，以及驱动力是什么。此外，在田间条件下也很难研究N2O排放和N输入之间的指数关系的过程和驱动因素，因为与N2O排放相关的过程是复杂和相互关联的。来自布伦斯韦格Thünen研究所和乔治·奥古斯特-哥廷根大学(GAU)的德国团队在利用15N示踪工具管理土壤和含水层中N2O周转的N转化和过程方面拥有丰富的经验。他们正在开发一种N2O同位素分馏方法，与在GAU建立的无氮(N_2)培养系统相结合，以估计土壤中的N_2通量，以及N_2O同位素比率法，以区分N2O的产生途径(例如，硝化作用、细菌反硝化作用和真菌反硝化作用)。借助中国和德国团队的互补专业知识，我们打算：1)建立新的稳健的方法，精确量化不同土地利用类型区域下直接氮素通量的永久脱氮速率；2)表征氮素生产、N2O排放和N2O/(N2O+N2)比值的时空变化；3)区分N2O的产生途径，并阐明长三角地区氮素去除的过程及其驱动力。所有合作伙伴之间的合作将是探索我们对与土壤中完整的N循环相关的复杂和相互关联的参数的理解的关键。我们期望这个项目能获得很高的科学回报和产出，解决目前公众高度关注的问题。

Delta region is a heavy N loading region with intensive agriculture where excess Nr causes various eco-environmental problems such as eutrophication of lakes, algal bloom, greenhouse effects, ground water pollution etc.. A recent N budget study of the Chinese team showed that more than half of the N load was lost permanently from terrestrial ecosystems, with nitrous oxide (N2O) emissions increasing exponentially with increasing N input. However, due to methodological difficulties in measuring all N products from the variety of underlying processes, it is unknown where and when this permanent N removal occurs and what are the driving forces. Furthermore, processes and drivers of the exponential relationship between N2O emission and N input are also difficult to study under field conditions as processes related to N2O emissions are complex and inter-related. The German teams from Thünen Institute in Braunschweig and Georg-August-Universität Göttingen (GAU) have extensive experience in N transformation and processes governing N2O turnover in soils and aquifers using 15N tracer tools. They are developing an N2O isotope fractionation method in combination with a dinitrogen (N2)-free incubation system set up at GAU to estimate N2 fluxes from soils, and the N2O isotopomer ratio method to distinguish production pathways (e.g., nitrification, bacterial denitrification and fungal denitrification) of N2O. With the complementary expertise of the Chinese and German teams, we intend to: 1) establish new robust methods to precisely quantify permanent N removal rates by direct N2 fluxes under different land-use type area; 2) Characterize the spatial and temporal variation of N2 production, N2O emission, and N2O/(N2O+N2) ratio; 3) distinguish the production pathways of N2O and elucidate the processes governing N removal in the Yangtze River Delta region and its driving forces. Collaboration between all partners will be the key to explore our understanding on complex and inter-related parameters related to complete N cycles in soil. We expect a high scientific reward and output of this project, dealing with issues currently of high public concern.