海南水稻-辣椒轮作土壤N2O排放规律及产生机制研究

Because of superior hot environment in Hainan Province, the rotation of vegetables in winter and subsequent rice cultivation is becoming the dominant cropping pattern in local, where specific managements (e.g., fertilizer, irrigation) and climate factors (e.g., temperature, rainfall) may result in the regional characteristics of N2O emissions. In order to fill the defects of studies on the N2O emission in tropical region, we will quantify N2O fluxes from rice-vegetable cropping plantations in Hainan Province using the field and incubation experiments as well as static chamber and gas chromatography techniques. The 15N tracing technique combined with Markov chain Monte Carlo (MCMC) numerical algorithm, gases inhibition method and next-generation pyrosequencing will be used to determine soil gross N transformation rates, pathways and the relevant key N functional microorganisms. The purposes are to 1) identify the characteristics and affecting factors of N2O emissions from rice-vegetable cropping plantations in different typical climatic regions in Hainan Province; 2) evaluate the contribution of different N transformations to N2O production and the driving mechanisms of functional microorganisms in N transformations and N2O emissions. These results will effectively complement the study deficiency of N2O emissions in tropical region, and provide the theory basis for exactly evaluating N2O emission and mitigation in tropical agricultural ecosystem.

海南形成的冬种瓜菜收获后植稻的轮作模式因管理及气候等因素与温带或亚热带地区的差异大，其土壤N2O排放可能有其区域特点。为弥补热带农田N2O排放的缺陷，本项目选取海南湿润及半湿润生态气候区水稻−辣椒轮作土壤作为研究对象，采用静态箱法通过原位监测，明确两生态气候区水稻−辣椒轮作土壤N2O的排放规律及其影响因素；采用15NH4NO3和NH415NO3同位素成对标记方法和气体抑制法，结合MCMC氮素转化模型和高通量测序等分子生态学手段，区分两生态气候区土壤氮转化过程对N2O排放的贡献及土壤微生物在驱动氮关键转化过程中的作用机理，以明确N2O产生机制。项目实施补充热区土壤N2O排放研究的不足，有助于深入认识热区水稻−瓜菜种植模式下土壤N2O排放规律、产生机制和影响因素，研究结果为准确评估热带地区农田N2O排放及减排提供理论依据。

海南形成的冬种瓜菜收获后植稻的轮作模式因管理及气候等因素与温带或亚热带地区的差异大，其土壤温室气体排放可能有其区域特点。为弥补热带农田温室气体排放研究的不足，选取湿润及半干旱生态气候区水稻冬瓜菜轮作土壤作为研究对象，研究土壤温室气体的排放规律及其影响因素、氮转化过程对N2O排放的贡献及土壤微生物在驱动氮关键转化过程中的作用机理。研究结果如下：.（1）水稻-冬瓜菜轮作土壤N2O排放主要集中在瓜菜季，排放量及排放系数高于内地旱地土壤。水稻季N2O排放也高于国内，但其CH4排放远低于国内稻田，可能源于目前水稻见干见湿的水分管理，使土壤难以形成强还原的土壤环境，达不到CH4产生的条件。.（2）湿润生态气候区，早稻N2O在施基肥后有较高排放，而晚稻N2O则在晒田期才有较高排放，这与当地早稻在旱季生长，晚稻在雨季生长有关。湿润气候区种植辣椒土壤 N2O排放高于半干旱气候区的豇豆季土壤排放。.（3）水稻-冬瓜菜轮作土壤温室效应的主要贡献是CH4。生态气候类型区的差异及同一类型区早晚稻季的差异造成CH4排放的差异。半干旱气候类型区排放总量低于湿润气候区，源于湿润区种植两季水稻。湿润气候区内，早稻季较晚稻季CH4排放量少。早稻CH4排放在水稻生育后期而晚稻CH4排放在生育前期。.（4）土壤N2O产生过程以氨氧化细菌起主要作用。施肥促进矿化及自养硝化作用，不排除其对N2O排放有一定的贡献作用。nirS基因与N2O排放量呈显著正相关，反硝化作用对N2O排放贡献大。稻田土壤NH4+通过影响甲烷氧化菌活性，导致CH4排放量降低。.（5）优化施肥能保证产量。施加氮肥在一定程度上降低了热区稻田CH4排放量。添加脲酶与硝化抑制剂联合施用的处理在提高系统产量的同时降低了N2O和CH4排放，是热带地区值得推广的增产、减施、减排的施肥模式。