秸秆及其生物质炭添加下稻田土壤团聚体生物物理与碳氮水及微生物分布变化表征

This project will be conducted with a rice paddy field experiment with soil amendment respectively of maize straw and maize straw biochar. Size fractions of soil water stable aggregates will be seperated and obtaiined with a wate dispersion and wet sieving protocol with least disturbing particular OM and microbes. Aggregate microstructure will be prtraited with micro/subscopy and micro tomography techniques of X-ray uCT and NMR cryo-porometry, forms and mlecular and isotopic composition of SOM in and between aggregates will be charcterized using in situ analysis wih FTIR and NMR as well as bulk chemistry, total and active mirocbial abundance and community composition as well as enzyme activtties will be determined with PCR-DGGE and pyro-sequencing techniques. For selected samples, Nano-SIMS will be performed for portraiting old and new OM in/between macro-aggregates. We aimed to explore the spatiial patetrn of OM, microbes and enzymes across aggregate fractions,try to relate such pattern to mcirostructure features among the diffrent fraction of aggregates. By doing so, we try to udnerstand the the impact ofstarw and straw biochar on mciroscale biogeographyy of soil OM, nutrients and mcirobes, and to show how bicohar helps build soil aggregates and enhance microbial abundance and activity while building C stock in the rice soils. This study will contribute to the understanding of microscale mechanism of biogeochemistry related to biophysics of soil aggregation and to provide information for soil improvement and sustainable OM maangement from crop straw for rice agriculture.

以玉米秸秆及其生物质炭添加下水稻土田间试验为对象，水分散分离制备水稳性土壤团聚体不同粒径组，比较研究其粒径质量组成、采用微形貌微结构分析法研究表面和内部形貌特点，有机碳物理和化学形态及分子/同位素组成特点，微生物丰度、多样性及酶活性特点，进一步采用NanoSIMS研究大团聚体的新碳-老碳相关分布，探讨不同性质有机物添加下土壤团聚体生物物理结构及其碳氮水及微生物保持的变化，刻画可视图像与表面、孔隙容积表示的团聚体物理结构与碳氮水生物微域分布格局的关系，揭示生物质炭改善土壤结构、改进生物健康而促进生态系统功能的团聚体微观机理，为认识水稻土生物物理与生物地球化学循环的联系，也为稻田可持续有机质管理和土壤质量提升提供科学依据。

秸秆还田是全球公认的循环农业废弃物、保持和提升土壤有机质的常规田间管理措施，相对于稻田新鲜秸秆还田可能导致甲烷排放增加，秸秆炭化正在日益受到关注和推广。但是，不同形态的秸秆还田对于土壤团聚体发育和土壤固碳的效应还未得到科学阐明。本研究布设了新鲜秸秆、秸秆厩肥和秸秆生物质炭等碳量(10 t ha-1)还田的处理，采集了还田后1-3年耕层（0-15cm）原状土样品，分析土壤有机碳含量，分离制备水稳性团聚体粒径组（2000-250um宏团聚体，250-53um微团聚体和53-2um粉砂粒颗粒和 <2um黏粒（该二者因黏粒质量分数较小常常归并），分析其中有机碳库分布及其微生物丰度、酶活性丰度，并对宏团聚体进行计算机断层扫面微形貌观测表征，分析构建有机碳分配与团聚体发育及其结构（孔度）的关系，结果表明，与新鲜秸秆相比，秸秆生物质炭还田大幅度(30%)增加土壤有机碳,促进宏团聚体发育和颗粒态碳的大幅度增加 （45%), 有机碳由矿物结合态为主转变为颗粒态 （POM）为主，来自秸秆生物质炭的稳定有机碳主要分布于宏团聚体，而微生物基因丰度、多样性也表现为宏团聚体高于微团聚体和未团聚细颗粒，宏团聚体相对于微团聚体的质量比与颗粒态碳对于矿物态碳 的优势可以诠释团聚体与有机碳的协同演进，土壤固碳容量因颗粒态碳的积累而大幅度提升，同时带来土壤土壤生物活性的改善。这一研究提示，秸秆炭化还田有利于快速重建土壤团聚体，扩大土壤固碳容量，改善土壤碳库和微生境多样性。研究证明，宏团聚体中孔度及连通性与土壤颗粒态碳的丰缺由密切的关联性，土壤固碳通过有机质-团聚体-微孔隙的关联而联系于土壤生态系统功能。研究再次证明，水稻土中宏团聚体 （和）微团聚体，尽管质量分数低于粉砂级分散颗粒，是土壤固碳和微生境的活跃微域；土壤固碳有助于土壤生物活性和生态系统功能提升。