高应答水稻CH4排放对CO2浓度升高和氮肥的响应机制研究

The rice cultivar with high response to CO2 concentration enrichment ([CO2] enrichment), can significantly increase rice grain yield, is probably preferred to be planted in the further for meeting the demand of food with the growing population. However, rice with high response to [CO2] enrichment also significantly increases the root biomass and the tiller number, which results in much more substrates for methanogenesis and much stronger plant-mediated CH4 transport capability, thus most likely promoting CH4 production and its emission. On the other hand, it possibly enhances the capability of rice root to O2 transportation and then promotes CH4 oxidation, which consequently decreases CH4 emission. Unfortunately, reports about the effect of [CO2] enrichment on CH4 emission and its influencing mechanism from the rice with high response to [CO2] enrichment are very scarce. By applying N-fertilization probably increases the grain yield of rice with high response to [CO2] enrichment further, but it also profoundly affects each process of the CH4 emission. This project is planning to base on the FACE (Free-air CO2 Enrichment) experimental setting, and there are two rice cultivars with high and low responses to [CO2] enrichment for the investigated objects. It will use the stable carbon isotope technique, combined with the analysis of molecular biology technology, to study the CH4 production, oxidation, transport and emission of the paddy field under the 3-level of N-fertilization, focusing mainly on CH4 production potential, pathways of methanogenesis, CH4 oxidation potential and fraction of CH4 oxidized, methanogens and methanotrophs. Results of this research will systematically not only elucidate the responses of each process of CH4 emission from the rice with high and low responses to [CO2] enrichment to elevated [CO2] and N-fertilization, but also the corresponding mechanism of the difference between the two rice cultivars. Moreover, it will provide important parameters to the model study for forecasting the possible changes in the atmospheric CH4 concentration in future.

高应答水稻在CO2浓度升高条件下显著增加产量，但也明显增加根系生物量和植株分蘖数，将导致更多的产CH4底物、更强的CH4传输能力，从而可能促进CH4产生与排放；也有可能增强根系的泌氧能力、促进CH4氧化，而减少CH4排放。目前有关CO2浓度升高对高应答水稻CH4排放影响及其机理的研究报道还严重缺乏。施用氮肥可能进一步增加高应答水稻产量，但也会深刻影响CH4排放的各个过程。本项目基于FACE平台，以高、低应答水稻为研究对象，拟采用稳定性碳同位素自然丰度法，并结合分子生物学分析技术，研究三种施氮水平下稻田的 CH4 产生、氧化、传输和排放，侧重于 CH4 产生潜力、产生途径、氧化潜力、氧化百分率、产甲烷菌和甲烷氧化菌的研究。其结果将系统阐明高、低应答水稻CH4排放各过程对CO2浓度升高和氮肥的响应规律及其差异机制，为预测未来大气中CH4浓度的可能变化的模型研究提供重要参数。

大气CO2浓度（[CO2]）升高和氮肥施用是稻田CH4排放的两个重要影响因素。以往有关[CO2]升高对稻田CH4排放的研究多侧重于对低应答品种排放通量的影响，很少涉及对CH4排放过程机理，特别是对高应答品种CH4排放过程机理的影响研究。此外，[CO2]升高条件下施氮对高、低应答水稻CH4排放影响及其机理的研究报道也严重缺乏。本项目基于FACE平台，以高、低应答水稻为研究对象，联合稳定性碳同位素自然丰度法和分子生物学分析技术，研究了[CO2]升高和氮肥施用对稻田 CH4产生、氧化、传输和排放的影响，着重突出它们对CH4排放过程机理及其微生物学机制的影响。.连续3年的大田及室内培养试验结果表明：[CO2]升高降低高、低应答水稻CH4排放11-59%，这主要是由于[CO2]升高减少高、低应答水稻CH4产生潜力17-81%，并增加高、低应答水稻CH4氧化潜力2-70%；而且[CO2]升高增加了高、低应答水稻土壤表面0-10 mm的O2浓度，减少了产甲烷菌群落丰度，进一步说明[CO2]升高可能降低CH4产生能力但有助于CH4氧化。整个水稻生长期，[CO2]升高能够同时降低高、低应答水稻土壤孔隙水中溶解的CH4浓度，降幅为26-71%。[CO2]升高促进高、低应答水稻生长，增加水稻分蘖数的同时，提高了高、低应答水稻的平均土壤Eh达2-40%。综上可见，[CO2]升高是通过增加高、低应答水稻分蘖数，增强O2向土壤表面的传输，提高土壤Eh，从而减少产甲烷菌群落丰度和CH4产生潜力并增加CH4氧化潜力，进而降低土壤孔隙水中CH4浓度，最终显著减少高、低应答水稻CH4排放。另外，施氮情况下，[CO2]升高均能够减少高、低应答水稻CH4产生潜力；不施氮条件下，[CO2]升高减少高应答水稻CH4产生潜力，但增加低应答水稻CH4产生潜力。同时，无论施氮与否，[CO2]升高均有增加高、低应答水稻CH4氧化潜力的趋势。.研究结果系统阐明了高、低应答水稻CH4排放各过程对[CO2]升高和氮肥的响应规律及其差异机制，为预测未来大气中CH4浓度的可能变化的模型研究提供重要参数。