浙江红壤性水稻土中水稻秸秆分解过程及其中碳氮去向机制

After late rice harvest, the rice straw is usually returned to field in Zhejiang province. The straw returned soil is usually used for fallow, planting green manure or rape, which could last to succeeding rice planting in the next year. We guess that the processes of rice straw decomposition and its carbon and nitrogen distribution may be different in three field management measures, which could be attributed to the different microbial community composition and/or function induced by different soil environment. However, little study has directly compared the decomposition mechanism of straw in three management measures, which influence our proper evaluation of the effects of straw returning on succeeding rice growth. In this project, the red paddy soil of Zhejiang province will be studied by field litterbag experiment and pot experiment. Using 13C-15N dual labelled rice straw, we will analyze the changes of soil environment, straw decomposition and nutrients releasing pattern as well as the changes of carbon and nitrogen structure based on nuclear magnetic resonance technique. We will also quantitatively evaluate the distribution of straw carbon and nitrogen in systems of soil-crop (green manure and rape) and define the microbial communities included in straw turnover. These research results will help us to further understand the decomposition mechanism and nutrient distribution of rice straw in different field management practices and provide a scientific basis for evaluating the potential effects of straw returning on soil fertility.

浙江地区晚稻收获后的秸秆往往直接还田，而还田土壤一般直接休闲、种植绿肥或油菜，及至来年水稻种植。我们猜测还田秸秆在这三种田间管理模式下的分解过程及其中的碳氮去向可能不同，这可能由于秸秆所处环境不同导致驱动秸秆分解的微生物组成和/或微生物功能发生变化所致。但目前很少研究直接比较秸秆在这三种管理模式下的分解机制，从而影响我们正确评估秸秆还田对下季水稻生长的影响效应。本项目以浙江红壤性水稻土为研究对象，通过田间尼龙网袋埋设试验和盆栽试验，利用13C-15N双标记水稻秸秆，分析不同田间管理模式下尼龙网袋外土壤环境变化、秸秆分解的动态变化、养分释放规律及基于核磁共振技术的碳氮结构变化；定量追踪秸秆碳氮在土壤-作物（绿肥、油菜）系统中的分布、明确参与秸秆转化的微生物群落。研究结果将进一步揭示水稻秸秆在不同田间管理模式下的分解机制和养分去向，为评估秸秆还田对土壤肥力的潜在影响提供科学参考。

浙江地区冬季稻田的管理措施一般为直接休闲、种植紫云英绿肥或者油菜。但目前不同管理措施如何影响还田水稻秸秆的分解过程以及内在的作用机制尚不明确。本项目通过田间尼龙网袋掩埋试验分析了不同管理模式下秸秆分解和养分释放的动态变化及土壤理化性质和微生物性质的变化；利用添加13C-15N双标记水稻秸秆的盆栽试验定量追踪秸秆碳氮在土壤-作物（绿肥、油菜）系统中的分布特征及土壤微生物群落特征。结果表明：（1）与休闲对照处理相比，秸秆分解四至七个月的过程中，种植紫云英和油菜显著增加了秸秆分解率和秸秆碳氮释放率。另外，种植紫云英和油菜均较休闲对照处理在秸秆分解五个月后改变了附着在秸秆上的细菌和真菌群落组成，其中种植紫云英能够增加细菌Terriglobus属和真菌Trichoderma属相对丰度。.（2）种植紫云英和油菜较休闲对照处理显著增加了土壤可溶性有机碳、热水提取态有机碳和微生物生物量碳含量以及纤维素酶、β-葡萄糖苷酶、蛋白酶和酸性磷酸酶活性。此外，种植紫云英和油菜显著提高了微生物功能多样性指数。高通量测序分析表明种植紫云英和油菜也改变了秸秆分解五个月后的土壤细菌和真菌群落组成，且细菌和真菌群落组成与土壤理化性质变化显著相关。种植紫云英能够特定富集细菌Pirellula属和真菌Chrysosporium属，而种植油菜能够特定富集真菌Psathyrella属。相关性分析表明秸秆分解率和碳氮释放率均与土壤酶活性、微生物功能多样性以及特定富集的微生物种群呈显著正相关关系。.（3）作物收获后，紫云英地上部和根吸收的秸秆氮量显著低于油菜吸收的秸秆氮量。种植紫云英和油菜较休闲对照处理显著增加了土壤热水提取态有机碳、微生物生物量碳和总有机碳中来自于秸秆碳的含量，显著降低了土壤可溶性总氮、颗粒有机氮和总氮中来自于秸秆氮的含量。种植紫云英和油菜较休闲对照显著增加了土壤纤维素酶、β-葡萄糖苷酶、蛋白酶和几丁质酶活性且改变了开花期和收获期的细菌和真菌群落组成，其中种植紫云英和油菜分别能够增加细菌Ramlibacter属和Anaecromyxobacter属相对丰度。