UV-B辐射和氮沉降耦合作用下水稻秸秆降解过程及其微生物驱动机制

Rice straw is one of the most important organic resources in agroecosystem. The decomposition of straw is mainly driven by soil microorganisms and greatly regulated by various environmental factors. Ultraviolet-B (UV-B) radiation and nitrogen (N) deposition are important environmental factors. However, little is known about the combined effects of them on the process of rice straw decomposition and its microbial mechanisms in red soil region. We will investigate the relationship between chemical structure and decomposition process of rice straw under the combined effects of UV-B radiation and N deposition, via a series of modern techniques such as scanning electron microscope, infrared spectroscopy and 13C cross polarization/ magic angle spinning nuclear magnetic resonance (CP/MAS NMR). The investigations will allow us to identify the key environmental factors regulating the decomposition process of straws. High-throughput sequencing will be applied to clarify the changes in decomposing microbial communities and the primary microbial taxa, and to elucidate the interaction between microbial community and decomposition process of straw. In addition, we will investigate the relationships among straw structure, decomposing microbial community and decomposition process of straw by bioinformatics methods, to elucidate the relative contribution of photodegradation and microbial decomposition. The aim of this study is to clarify the combined effects of UV-B radiation and N deposition on rice straw decomposition and its microbial mechanisms, such efforts will benefit to the reclamation management of plant straw under global change.

水稻秸秆是我国稻田重要的有机资源，其降解过程主要由微生物所驱动，且受到多种环境因子的影响。UV-B辐射增强和氮沉降及两者耦合作用对南方红壤区水稻秸秆降解过程的影响及其微生物驱动机制尚不清楚。本项目拟借助扫描电镜、红外光谱和交叉极化/魔角旋转核磁共振等技术，研究UV-B辐射增强和氮沉降条件下水稻秸秆结构变异与秸秆降解过程的关联，阐明调控水稻秸秆降解过程的关键环境因子；利用高通量测序等现代生物学手段，探明水稻秸秆降解过程中微生物群落演变规律及其关键微生物类群，揭示UV-B辐射增强和氮沉降条件下水稻秸秆降解动力学过程与微生物群落的内在关联；结合生物信息学分析方法，构建水稻秸秆结构、降解微生物群落和降解过程之间的对应关系，阐释秸秆光降解和微生物降解的相对贡献。研究结果将明确UV-B辐射增强和氮沉降对水稻秸秆降解的影响及其微生物驱动机制，为全球变化条件下我国秸秆资源化利用提供科学依据。

本项目以水稻秸秆为研究对象，通过一年的野外降解实验，揭示UV-B辐射和氮沉降条件下秸秆的化学官能团变化，建立了化学组成与微生物群落之间的内在关联，阐明了UV-B辐射和氮沉降条件下秸秆降解的微生物驱动机制。主要结论如下：（1）UV-B辐射增强和氮沉降均促进了水稻秸秆的降解，两者的耦合作用对秸秆降解的促进作用更加明显，UV-B辐射增强和氮沉降耦合处理C/N下降最快，降低至15左右；（2）秸秆降解过程尤其是降解后期显著改变着秸秆的化学官能团相对含量。增强UV-B辐射和氮沉降均加快了含氧烷基和二氧烷基的降解，加速了烷基碳和羰基碳的累积；（3）Biolog结果表明，在降解第6个月，N沉降对微生物AWCD值的影响较小，而UV-B辐射可以提高秸秆降解微生物AWCD值。降解12个月，UVB辐射和N沉降均显著提高微生物碳源利用能力；（4）通过高通量测序技术分析了秸秆降解细菌和真菌群落的演变规律。增强UV-B辐射和N沉降对变形菌、酸杆菌、绿弯菌、拟杆菌和厚壁菌和芽单胞菌门产生了显著的影响，而硝化螺旋菌门受到了UV-B和氮沉降之间交互作用的影响。方差分解分析表明N沉降和降解时间对细菌群落变化的解释量最大，分别为14.0%和13.4%，UV-B辐射增强对细菌群落变化的解释率为7.8%。子囊菌门、被孢霉门、担子菌门是秸秆降解主导的真菌类群。UVB和UVBN处理中子囊菌门、担子菌门和毛霉菌丰度高于N处理和对照组。但是UVB和UVBN处理被孢霉门丰度明显低于对照。（5）典范对应分析表明，在降解过程中秸秆化学官能团与细菌和真菌群落之间关系密切，含氧烷基和二氧烷基在秸秆降解6个月时影响最大。到了后期，芳香类化合物以及烷基等难以被微生物降解的基团对细菌和真菌群落影响较大。（6）网络分析结果显示参与降解秸秆含氧烷基和二氧烷基的基团降解的细菌以变形菌门为主，真菌以子囊菌门、担子菌门和单毛壶菌门为主。上述研究成果为全球变化条件下我国秸秆资源化利用提供了科学基础。