增强UV-B辐射对元阳梯田稻田甲烷排放的影响与机理研究

The rice paddy in Yuanyang Terrace was typical year-round flooded paddy in Southwest China. There was continuous and large amount methane emission from year-round flooded paddy. The significant effects of UV-B radiation on methane emission from rice paddy had been studied; however the effects and mechanisms of UV-B radiation on the methane emission from year-round flooded paddy were rarely studied. In this project the rice paddy in Yuanyang Terrace will be chosen as study object. 1) to investigate the effects of UV-B radiation on the methane production, oxidation and emission flux under enhanced UV-B radiation by closed chamber experiment, in which the methane concentration will be continually monitored by gas chromatography method after the methane oxidation has been inhibited by C2H2. 2) to investigate the effects of enhanced UV-B radiation on quantity and components of rice straw and root exudates, oxygen content, methanogen and methanotroph community structure in rhizosphere by field experiment. 3) to explore the possible ways and mechanisms of enhanced UV-B radiation on methane emission from rice paddy according to the effects of enhanced UV-B radiation on the quantity and components of rice straw and root exudates, oxygen content, methanogen and methanotroph community structure in rhizosphere. The results will offers a new knowledge about the emission characteristics and change trend of greenhouse gases from agro-ecosystem under enhanced UV-B radiation, and enrich the theory of UV-B radiation ecology and greenhouse gases emission from farmland, which has important significance both in theory and in practice.

元阳梯田稻田是我国西南地区典型的冬水田，冬水田具有持续和大量排放甲烷的特点。UV-B辐射对稻田甲烷排放有显著影响，但UV-B辐射对冬水田甲烷排放的影响及其机理的认识有限。项目以元阳梯田稻田为研究对象，模拟UV-B辐射增强，开展田间静态箱培养试验，通过施加乙炔抑制甲烷的氧化，并采用气相色谱法测定甲烷浓度的变化，定量研究增强UV-B辐射对稻田甲烷产生量、氧化量与排放通量的影响。并通过大田试验研究增强UV-B辐射对水稻根系分泌物的数量与组分、根际氧气含量、甲烷产生菌与氧化菌群落结构的影响。从影响水稻根系分泌物的数量与组分、根际氧气含量、甲烷产生菌与氧化菌群落结构的角度，探讨增强UV-B辐射影响元阳梯田稻田甲烷排放的可能途径与机理。为地表UV-B辐射增强情景下农田生态系统温室气体排放规律与变化趋势提供新的认识，丰富UV-B辐射生态与农田生态系统温室气体排放的理论与认识，具有重要的理论与实践意义。

该项目在元阳梯田海拔1600 m稻田种植农家品种水稻“白脚老粳”，模拟UV-B 辐射增强(5.0 and 10.0 kJ/m2)，开展3 年的田间原位观测和室内测定分析，研究增强UV-B辐射对稻田甲烷排放通量、水稻植株通气组织、根系低分子量有机酸的分泌量、水稻根际土壤甲烷产生相关古菌群落结构的影响。结果表明：（1）UV-B辐射增强导致水稻根系横切面积和维管束面积增加，植株茎壁横切面积的气腔和维管束面积增大。（2）UV-B辐射增强导致水稻根系草酸和琥珀酸的分泌量增加，酒石酸和苹果酸的分泌量降低。（3）自然光照和UV-B辐射增强处理间的水稻根际古菌和产甲烷古菌群落结构没有明显差异。根际古菌以杂古菌MCG (Miscellaneous Crenarchaeotic Group)、MBGD广古菌 (Marine Benthie Group D)、甲烷鬃毛菌(Methanobacterium)、ASC21、TMG (Terrestrial Miscellaneous GpTMCG)等为优势菌；产甲烷菌群有甲烷鬃毛菌、反刍甲烷杆菌(Methanobacterium)、Methanoregula、甲烷微球菌(Methanomicrobiaceae)、甲烷八叠球菌属(Methanosarcina)、Methanomassiliicoccus、甲烷杆菌(Methanobacteriaceae)等。（4）UV-B辐射增强不改变稻田甲烷排放的季节性变化规律，但导致拔节孕穗期和灌浆成熟期的稻田甲烷排放通量，及全生育期稻田甲烷累积排放通量显著增加。（5）水稻根系草酸的分泌量、植株通气组织的部分性状与稻田甲烷排放量呈显著正相关。表明UV-B辐射增强促进元阳梯田稻田甲烷排放增加，与其改变水稻植株通气组织、根系分泌低分子量有机酸相关。项目已发表2篇SCI论文、6篇中文核心和1篇会议论文，培养硕士研究生1名；课题组成员参加了6次国内学术会议。