UV-B辐射对稻田土壤活性有机碳和甲烷产生周年动态的影响与机理

Enhanced ultraviolet-b (UV-B) radiation on earth surface is one of the important issues in the research on global climate change. UV-B radiation has a remarkable effect on methane emission from rice paddy. However, present researches focus on rice growing period and are lacking on annual period. Yuanyang Terraces is located in Yunnan plateau with a strong UV-B radiation. There is a continuous and large amount methane emission from year-round flooded rice paddy with straw return in fallow period. In this project the rice paddy in Yuanyang Terrace will be selected as study object. Under enhanced UV-B radiation, we will carry out some experiments include field plot, hydroponics, root bag cultivation, straw decomposition, etc. The research objects include: (1) To clarify the effects of UV-B radiation on annual dynamics of soil active organic carbon and methane emission in rice paddy. (2) To study the effects of UV-B radiation on chemical composition of root exudates and straw in rice growing period, and decomposition of straw in fallow period; then to expound the effects of changes of root exudates components and straw decomposition on soil active organic carbon turnover and potential methane production that inducing by UV-B radiation. (3) To establish the relationship between soil active organic carbon turnover and methane producing dynamics in rice paddy. (4) To reveal the processes and mechanisms of UV-B radiation on annual dynamics of soil active organic carbon and methane production in rice paddy as a result of the changes of root exudates components and straw decomposition under UV-B radiation. The results will offers a novel knowledge on the emission pattern and trend of greenhouse gas from agro-ecosystem under enhanced UV-B radiation, and enrich the theory on UV-B radiation ecology and carbon cycle in agro-ecosystem.

地表UV-B辐射增强是全球气候变化研究的重要问题之一。UV-B辐射对稻田甲烷排放有显著影响，但目前研究关注了水稻生长期，缺少周年的研究。元阳梯田地处UV-B辐射较强的云南高原，稻田全年淹水、秸秆还田，终年持续、高通量的排放甲烷。项目拟以元阳梯田稻田为研究对象，模拟UV-B辐射增强，开展大田、水培、根袋培养、秸秆分解等试验，明确UV-B辐射对稻田土壤活性有机碳和甲烷排放周年动态的影响。研究UV-B辐射对水稻生长期根系分泌物和秸秆化学组成、休闲期还田秸秆分解的影响，进而明确UV-B辐射改变根系分泌物组成和秸秆分解，对土壤活性有机碳周转和甲烷产生的影响，解析土壤活性有机碳组分周转与甲烷产生动态的关系，揭示UV-B辐射影响稻田土壤活性有机碳与甲烷产生周年动态的过程与机理。研究结果为UV-B辐射增强情景下农田温室气体产生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碳循环方面的理论。

项目以元阳梯田稻田为研究对象，模拟UV-B辐射增强，开展大田、水培、根袋培养、秸秆分解等试验，研究UV-B辐射影响水稻根系分泌物、秸秆化学组成与还田分解，进而影响稻田土壤活性有机碳和甲烷排放周年动态的过程与机理。结果表明：（1）UV-B 辐射增强显著影响稻田土壤碳转化酶活性、功能基因表达、活性有机碳含量与甲烷排放，增加稻田土壤纤维素酶活性、甲基辅酶还原酶基因相对表达量、以及溶解性有机碳含量，降低稻田土壤多酚氧化酶和蔗糖酶活性、甲烷单加氧酶功能基因相对表达量、微生物量碳和易氧化有机碳含量和水稻生长期稻田甲烷的排放通量。（2）UV-B辐射显著改变水稻根系分泌物组分的含量，导致水稻根系分泌物中游离氨基酸、可溶性糖、总酚、草酸和琥珀酸的含量增加，苹果酸含量降低；进而导致水稻根际土壤草酸、琥珀酸和总有机酸含量显著增加，苹果酸和酒石酸含量显著减少。且水稻根系分泌物组分与稻田土壤甲烷产生关系密切，添加UV-B辐射下生长的水稻根系分泌物及其组分（可溶性糖、低分子量有机酸）会显著改变土壤碳转化酶活性、活性有机碳含量、甲烷产生菌丰度，提高土壤甲烷排放通量。（3）UV-B辐射会改变水稻秸秆化学组成与还田分解，显著增加水稻秸秆木质素、总酚和类黄酮的含量，促进还田秸秆组分的木质素、纤维素、半纤维素和水溶酚的降解；进而影响稻田土壤活性有机碳转化与甲烷排放，导致土壤碳转化酶活性、活性有机碳含量与甲烷排放通量降低。总之，UV-B辐射增强改变水稻根系分泌物组分含量与还田秸秆分解，影响稻田土壤碳转化酶活性、活性有机碳周转、甲烷产生菌丰度与功能基因表达，进而降低稻田甲烷排放。该研究探讨了土壤活性有机碳组分周转与甲烷产生动态的关系，揭示UV-B辐射影响稻田土壤活性有机碳与甲烷产生周年动态的过程与机理。结果为UV-B辐射增强情景下农田温室气体产生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碳循环方面的理论。项目已发表论文12篇，其中SCI论文5篇，培养硕士生3人，参加国内外学术会议8次。