亚热带丘陵区氨气近源沉降特征、影响机制及其土壤N2O排放效应

Agriculture is the major source of ammonia (NH3) emissions. The neighborhoods of ammonia emission sources may be the hotspots of NH3 deposition due to the high atmospheric NH3 concentrations. However, the deposition rates and impact factors for the NH3 deposited around the sources are still less know. NH3 (other than NH4+) is the direct substrate of the first step of nitrification, and thus the deposited NH3 in the neighborhood of emission sources may act directly in the nitrification process and promote soil N2O emissions, but this is still not proved directly by experiments. In this study, typical NH3 emission sources of croplands and animal feedlots/houses and their neighboring areas will be chose as the study objects, NH3 deposition around the neighborhood of emissions sources will be measured in situ to characterize the spatial and temporal variations of NH3 deposition. The NH3 emission intensities of cropland sources will be measured and the emission intensities of animal feedlots/houses will be estimated simultaneously, and meteorological factors and surface plant types will also be monitored so as to find out the key mechanisms of the impacts of source intensities, meteorological factors and surface plants on the NH3 deposition in the neighborhood of sources. Soil N2O emission will also be measured in the neighborhood of NH3 sources to calculate the soil N2O emission factors caused by NH3 deposition. By using the 15N labelled NH3 fumigation experiment, soil inorganic nitrogen content, soil nitrification activity, N2O emissions and ammonia oxidation bacteria and archaea gene abundances and community structures will be measured to clarify the mechanism for the coupling between NH3 deposition and soil N2O emissions. The proposed project will contribute to confirm the fate of emitted NH3 and its environmental impacts, and thus provide scientific base for NH3 emission mitigation.

农业是氨气主要排放源，排放源周边氨浓度高可能是氨沉降热区，但其沉降量及影响机制仍不尚清楚。氨是硝化反应直接底物，在排放源周边沉降的氨可能会直接参与硝化过程，促进N2O排放，目前尚缺乏直接证据。本研究以亚热带丘陵区典型种植业（稻田、茶园、蔬菜地）和养殖业（养猪/牛/鸡场）氨气排放源及其周边区域为研究对象，原位监测排放源周边氨沉降，揭示氨沉降量的时空变异。同步观测种植源和估算养殖源氨排放强度、观测气象因子和源周边下垫面植被状况，采用多元统计分析方法，研究源强、气象因子及下垫面植被对氨近源沉降影响的关键机制。同步观测源周边土壤N2O排放通量，获取氨沉降的土壤N2O排放系数；进一步采用15N标记的氨熏蒸模拟实验，研究土壤无机氮动态、硝化速率、N2O排放及土壤氨氧化细菌及古菌的基因丰度及群落结构，阐明沉降氨与土壤N2O排放的耦合机制。项目将有助于厘清氨气排放后的去向和环境影响，为氨减排提供科学依据。

农业是氨气主要排放源，排放源周边氨浓度高可能是氨沉降热区，但其沉降量及影响机制仍不尚清楚。氨是硝化反应直接底物，在排放源周边沉降的氨可能会直接参与硝化过程，促进N2O排放，目前尚缺乏直接证据。本研究以亚热带丘陵区典型种植业和养殖业氨气排放源及其周边区域为研究对象，原位监测排放源周边氨沉降，揭示氨沉降量的时空变异。同步观测种植源和估算养殖源氨排放强度、观测气象因子和源周边下垫面植被状况，采用多元统计分析方法，研究源强、气象因子及下垫面植被对氨近源沉降影响的关键机制。同步观测源周边土壤N2O排放通量，获取氨沉降的土壤N2O排放系数；进一步基于模拟培养实验阐明沉降氨与土壤N2O排放的耦合机制。.研究发现，稻田、集约化养猪场和养牛场周边均存在较高的氨气浓度及氨沉降量，且氨气浓度与沉降量均随距离养殖场距离的增加而呈指数下降。丘陵区典型稻田（0.6 ha）下风向100 m范围内氨气沉降量约占挥发量的80%。丘陵区一存栏量为900的奶牛场氨排放量高达26300 kg N yr-1，奶牛场500m范围氨总沉降量为4100 kg N yr-1，占氨总排放量15.5%。丘陵区典型集约化养猪场（年存栏量平均为8900头）一年中的氨气总排放量和500m范围近源沉降量分别为63000 kg N yr-1和5400 kg N yr-1，氨气年近源沉降占到氨气年排放的8.6%。下垫面类型、风向、气温对近源沉降量均有显著影响。.近源氨沉降提高了土壤无机氮含量和N2O排放量，养猪场周边N2O排放量在0.31-1.48 kg N ha-1，占到氨沉降的0.98%-1.94%，平均为1.46%。添加尿素N2O排放显著高于添加硫酸铵和硝酸钾，表明NH3相较于NH4+更有利于促进土壤N2O的生成。.本研究表明集约化养殖场是重要的氨气排放源，氨气近源沉降对养殖场周边产生较高的氮输入，从而会对养殖场周边生态系统产生重要影响。而集约化养殖场周边较低的近源沉降比例，也表明集约化养殖场排放的氨气大部分会进入大气，从而对大气氨污染具有重要贡献。不同类型排放源，近源沉降比例随氨气排放强度的增加而减少，表明种植/养殖规模对氨气的近源消纳具有重要影响。