外源有机物质提升典型旱作土壤有机质的微生物介导机制研究

The concentration of soil organic carbon in Chinese arable soils is rather low compared with those in USA and European countries, which considerably suppresses the increase of crop yields due to insufficient supply of nutrients and water and lower fertilizer nitrogen use efficiency. Up to date, however, the process of organic carbon accumulation in soils is not well understood, which in turn limits the development of effective practices for improving soil fertility. In the present study, soil samples from three long-term field experiments where organic manure and inorganic fertilizer have been applied will be collected at the Yingtan, Fengqiu and Hailun Agro-ecological experimental stations and then separated into different size aggregates through wet-sieving. The concentration and components of organic matter will be measured in the silt plus clay fraction to understand the accumulation processes of organic matter and its relation to aggregation. The components, molecular structure, stability and sources of organic matter in different size aggregates will also be analyzed using the chemical method and nuclear magnetic resonance technique to understand the distribution and regulation of organic carbon among aggregates. The community structure of microorganisms in soils and aggregates will be determined using the macro genomics, and its relation to organic carbon concentration in soil and aggregates will be evaluated. The relationship between microbial community structure and soil porosity or oxygen diffusion rate will be elucidated. The laboratory incubation with addition of 13C-labelled cellulose to long-term field experimental soils and field experiment with 13C-labelled wheat straw at the Yingtan, Fengqiu and Hailun Agro-ecological experimental stations will be set up. The transformation process of 13C in soils by microorganisms will be monitored by the 13C nucleic acid probe and distribution of 13C in aggregates will be measured to evaluate the influence of soils with different organic carbon concentrations on the residual rate of exogenous organic carbon and the kind of functional microorganisms coupling to decomposition of exogenous organic material. The decomposition rate of added organic material in soils at different regions, and the sources and allocation process of newly formed organic matter in aggregates will be examined. The objective of this study is to understand the accumulation processes of organic carbon and how microorganisms transform exogenous organic material into soil organic matter. Based on this study, effective practices for increasing organic matter in upland soils will be suggested according to soil characteristics especially components of native organic matter.

我国土壤有机质含量较低，已成为高产作物品种潜力发挥和水肥高效利用的主要限制因素。然而土壤有机质如何转化，外源有机物质如何有机质化并在土壤中累积，机制尚不清楚。项目拟选取长期定位试验土壤，利用团聚体分级、核磁共振等技术，研究粉粘粒组分中有机质累积特征与团聚体的关系，解析团聚体形成的关键控制因素；采用高通量测序、CT等技术，研究土壤孔隙等性质、微生物群落特点，阐明土壤肥力梯度上微生物群落演替规律及其与有机质和团聚体的耦联关系；建立13C-有机物质微宇宙和微区试验，利用DNA-SIP等技术，研究有机物质13C转化的功能微生物群落和活性，阐明微生物的接力利用机制和相对贡献；利用生物标志物、nanoSIMS等技术，研究有机物质13C在不同土壤中的分解速率、代谢产物来源和在团聚体中分配过程及其与微生物的阻隔关系，揭示有机物质提升土壤有机质的效应及机制，阐明有机质累积规律，为土壤有机质调控提供理论依据。

我国农田土壤有机碳含量仅为农业先进国家的2/3，严重制约作物产量提升。选取有机无机肥长期试验红壤和潮土及百年尺度不同开垦年限农田黑土，围绕有机碳含量、组分、团聚体形成、微生物群落结构演替、外源碳转化的微生物机制和累积规律等展开研究。土壤有机碳含量的增加主要通过难分解有机组分多肽、几丁质、芳香碳等累积实现，是由于团聚化降低氧分压，抑制多酚氧化酶活性所致；植物组分碳和微生物残留碳随土壤有机碳含量增加而增加，但是植物组分碳占比保持20%不变，相反微生物残留碳占比不断降低，因此土壤有机碳的累积主要依赖外源有机肥施用；大团聚体质量占比随土壤有机碳增加呈指数增加，最大值为70%。但是占比在有机碳小于30g/kg的土壤中呈线性增加，表明此含量可能是大团聚体形成快慢转折的临界值；细菌和真菌基因丰度随有机碳增加呈先增后降，群落结构也由低碳利用型物种向高碳利用型物种演替。随着土壤有机碳增加，细菌变形菌门、芽单胞菌门等相对丰度增加而绿弯菌门和酸杆菌门降低，真菌子囊菌门和球囊菌门增加而担子菌门降低。不同粒径团聚体中细菌和真菌丰度存在显著差异，有机碳含量增加降低团聚体中细菌绿弯菌门、放线菌门和真菌担子菌门丰度，增加细菌拟杆菌门和真菌子囊菌门丰度；有机碳含量越高的土壤中纤维素碳的残留率越低，是由于丰富的子囊菌纲能够强烈解聚纤维素链结构，革兰氏阴性菌则高效接力利用，导致纤维素碳大量损失；小团聚体中真菌基因丰度最高，是纤维素同化的主要场所。纤维素C的分配为小团聚体>微团聚体、粉粘粒组分>大团聚体， C首先进入小团聚体，再向粉粘粒组分迁移，高肥力土壤中13C再不分配弱于低肥力土壤；低肥力土壤中碳主要依赖矿物的化学保护，高肥力土壤中空间阻隔是碳主要的稳定机制；生物炭提高有机碳含量是由于芳基碳、酚基碳等难分解碳累积，降低细菌丰度，诱导微生物群落向碳矿化率低的细菌和真菌演替所致。秸秆还田平均增加我国旱地土壤有机碳16%，北方优于东中部，随秸秆输入量和土壤pH增加而增加。研究成果为土壤有机质培育技术研发提供了理论。