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

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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.