秸秆还田和根系及其分泌物对潮土有机质累积和团聚体形成的协同作用机制

Huang-Huai-Hai Plain locates in the northern China and is an important food supply area in China. In this area, the typical soil is classified as fluvo-aquic soil，the soil properties are generally presented as lower soil organic matter and poor soil structure with high sand, therefore, it is difficult to accumulate soil organic matter and to form aggregates in fluvo-aquic soil. A long-term fertilization experiments lasted for more than 20 years showed that soil organic matter could only reach to 10g/kg when only depending on the inputs of crop root and its exudates, however, application of organic fertilizers from straw decomposition could further significantly improve soil organic matter and soil structure. In this proposed project, pot experiments, laboratory culture experiments and field experiments will be conducted, via isotope labeling to study the cooperative effects of straw return and root and its exudate on soil organic matter accumulation. A series of modern techniques such as scanning electron microscope-X energy dispersive spectrometer(SEM-EDX), High-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR), high-throughput sequencing, and polymerase chain reaction (PCR) will be applied together to investigate the effects of soil organic matter and soil microbiology on the formation of aggregates. The aim of this study is to reveal the cooperative effects of straw return and root and its exudate on soil organic matter accumulation and aggregate formation in fluvo-aquic soil, Such efforts not only contribute to our further understanding of the soil organic matter and soil structure in different spatial and temporal scales, but also provide theoretical basis and technical support for the soil fertility cultivation of the Huang-Huai-Hai Plain.

我国粮食重要产区黄淮海平原潮土地区土壤有机质含量普遍较低且难于累积，土壤砂粒含量高使得土壤结构差且团聚体难以形成。前期长达20多年的长期定位施肥试验表明依赖于作物根系及其分泌物，有机质只能达到10g/kg而难以继续增加，而增施秸秆堆腐而成的有机肥则能进一步显著提升土壤有机质，改善土壤结构。因此，本项目通过野外盆栽、室内模拟以及大田长期定位试验，采用同位素示踪来研究秸秆和根系及其分泌物对土壤有机质的协同累积作用；利用同位素示踪、扫描电镜-X射线能谱仪结合技术(SEM-EDX技术)、高分辨魔角核磁共振（HR-MAS NMR）、高通量测序和实时定量PCR等技术来研究秸秆和根系及其分泌物协同作用下土壤有机质和土壤微生物对土壤团聚体形成机制的影响。以期在不同空间及时间尺度上阐明秸秆还田和根系及其分泌物对潮土有机质累积和团聚体形的协同作用机制，为黄淮海平原地区土壤地力的培育提供理论基础和技术支持。

我国粮食重要产区黄淮海平原潮土地区土壤有机质含量普遍较低且难于累积，土壤砂粒含量高使得土壤结构差且团聚体难以形成。前期长达20多年的长期定位施肥试验表明增施秸秆堆腐而成的有机肥则能显著提升土壤有机质，改善土壤结构。因此本项目目的在于揭示秸秆和根系及其分泌物协同作用下土壤有机质和土壤微生物对土壤团聚体形成机制。结果表明：（1）在典型潮土区河南省，1981年至2011年，土壤有机碳密度（SOCD）和土壤有机碳库（SOCP）呈明显的增长趋势。河南省实施秸秆全还田面积比例大于55%，约占总耕地面积的60.81%，为482万hm2。（2）经过180天培养，大部分秸秆（80%以上）被降解。利用固体13C CP/MAS核磁共振技术，试验前期不同处理间玉米秸秆碳基团差异较大，而随着时间延长差异逐渐缩小。秸秆碳水化合物优先分解，而芳香族化合物较难分解。潮土微生物群落结构随培养时间改变。细菌群落的组成对有机质的提升效果有一定的影响，潮土中酸杆菌门细菌群落结构利于有机质的提升。（3）秸秆还田能显著增加土壤有机质及其各组分的含量，促进有机质的累积并提高其稳定性。秸秆还田的同时施用肥料效果更佳，其中有机肥与秸秆混施效果优于化学肥料与秸秆混施。（4）生育期对玉米和小麦根系干重有显著影响，玉米和小麦根系量主要集中在0-20 cm土层中，并且占0-100 cm根系总量的范围分别为55.4～70.1%和57.6～78.6%；玉米、小麦根系生物量有机碳总量的值分别为361.46～886.65 kg/hm2和680.55～1314.93 kg/hm2。（5）土壤机械稳定性团聚体主要分布于>2000μm粒级中，而水稳性土壤团聚体主要分布于250-2000μm，秸秆还田能够促使土壤团聚体粒径由53-250μm向250-2000μm转移。土壤有机碳主要包含在250-2000 μm和53-250 μm粒级水稳性团聚体中，激发式秸秆能显著增加土壤有机碳。激发式秸秆深还主要增加细大团聚体（ 250-2000 μm ）中的fPOC和微团聚体（ 53-250 μm ）中的oPOC，且该土层中，团聚体中的有机碳主要由MOC组成。