稻田与鱼/蟹养殖湿地甲烷和氧化亚氮排放的观测比较研究

Methane (CH4) and nitrous oxide (N2O) are two key atmospheric greenhouse gases (GHGs) contributing to global warming. Current shift in agricultural production regime has a high potential in atmospheric GHGs mitigation . This study will be carried out in typical fish/crab farming wetlands，which were converted from conventional paddy fields for more than 5 yrs and 1 yr transition periods, respectively, and with the coventional paddy fields as control in Jiangsu area. Annual fluxes of CH4 and N2O are simultaneously measured under the three agricultural production regimes. The study will address the following items as listed:(ⅰ) To reveal the annual and interannual dynamics of ecosystem carbon and nitrogen processes as well as their underlying driving mechanisms in conventional paddies and fish/crab farming wetlands. (ⅱ) To evaluate the effects of agricultual land use shifting from conventional paddy fields to fish/crab cultured wetlands on mitigation of the net global warming potential derived from CH4 and N2O on different transition time scales and their consistency.(ⅲ) To reveal the soil microbial mechanisms associated with CH4 and N2O emissions under different agricultural wetland ecosystems. The results of this study would be conducive to reasonal estimation of CH4 and N2O emissions from agricultural wetland ecosystems, and simultaneously provide scientific basis and original data support for seeking the optimal agricultural wetland production regime to mitigate CH4 and N2O emissions derived from agriculture in China.

甲烷（CH4）和氧化亚氮（N2O）是大气重要温室气体，农业生产方式转变对大气温室气体减排具有较大潜力。本项目以江苏地区典型的常规稻田和长期（＞5年）和近期（1年）由稻田转变来的鱼/蟹养殖湿地为研究对象，通过对常规稻田、鱼塘和蟹塘湿地CH4和N2O的排放通量的原位观测和比较研究。项目将完成：（1）揭示稻田、鱼塘和蟹塘湿地生态系统碳氮过程的周年和年际动态特征及驱动机制；（2）评估常规稻田转变为鱼/蟹养殖湿地对减缓农业源CH4和N2O排放的长期和短期潜力及其一致性；（3）揭示不同农业湿地生态系统土壤碳氮与CH4和N2O排放的微生物学关联机制。研究结果将有助于合理评估我国农业湿地CH4和N2O的排放强度，为寻求常规稻田利用方式转变减缓农业源CH4和N2O排放提供科学依据

湿地是全球大气温室气体甲烷（CH4）和氧化亚氮（N2O）的重要排放源。本研究采用静态暗箱-气相色谱法原位同步观测和比较常规稻田和相邻蟹/鱼养殖湿地CH4和N2O排放，探讨不同农业湿地温室气体的排放强度、排放特征、驱动机制和综合温室效应等。试验包括：2013-15连续两年稻麦轮作周期，不同施氮量对稻田CH4和N2O排放的综合影响；2013-15连续两年养殖周期，综合研究蟹塘养殖湿地CH4和N2O排放；2014-15鱼塘养殖湿地全年养殖周期CH4和N2O排放原位观测；基于2013-15年稻田和蟹/鱼养殖湿地温室气体排放的研究结果，综合评估稻田转变为蟹/鱼养殖湿地的温室气体减排潜力和经济效益；利用试验蟹塘和鱼塘养殖湿地原位观测结果，初步估算我国和世界淡水养殖湿地CH4和N2O的全年排放总量。常规稻田转变为蟹/鱼养殖湿地可以同步实现降低农业源温室气体排放和增加农民收入的双赢目标。常规稻田转变为蟹/鱼养殖湿地能够明显降低全年CH4和N2O排放及其综合温室效应（GWP），其中N2O减排效果最为显著。在100年的时间尺度上，全年综合GWP：常规稻田 > 鱼塘养殖湿地 > 蟹塘养殖湿地；全年经济净收益：蟹塘养殖湿地 > 鱼塘养殖湿地 > 常规稻田；单位综合温室效应净收益：蟹塘养殖湿地 > 鱼塘养殖湿地 > 常规稻田。基于本研究结果，我国淡水养殖湿地饲料N的N2O-N转化系数为0.35-0.66%，与淡水生态系统外源N的CF-N相近；N2O直接排放系数在0.18-1.64 g/kg（单位养殖产量）之间。2013年我国淡水养殖湿地CH4和N2O-N全年排放量分别为0.24 Tg和5.7 Gg，分别占全国稻田CH4和N2O全年排放总量的3.0%和6.1%。2012年世界淡水养殖湿地N2O-N排放量为13 Gg，分别占全球淡水生态系统和人为总排放源的1.9%和0.2%。湖北、广东、江苏、湖南、江西、安徽和山东是我国淡水养殖湿地CH4和N2O排放的重点省份；中国、印度、日本和越南等国家是世界淡水养殖湿地N2O排放的热点区域。