基于示踪技术的土壤微食物网对长期秸秆还田潮土有机碳影响的研究

Straw return is an important way to increase the content of organic carbon in fluvo-aquic soil. However, its biological driving mechanism is not yet clear. As an important part of the soil ecosystem, soil micro-food web participates in many ecological processes such as organic carbon decomposition and nutrient cycling. In this project, the micro-food web of fluvo-aquic soil after the long-term straw returning will be studied in a microcosm with 13C isotope-labeled corn straw return. Cobalt-60 gamma (Co60γ) irradiation method was used to remove all nematodes in the soil. And then, nematodes suspension with different densities wil be added again in order to investgate the interactions between the nematodes and the microorganisms. The aims of this study are to understand (1)the interactions between soil nematodes and microorganisms in soil micro-food webs, (2) the mechanisms of these interactions on the stability of soil organic carbon, and (3) the functional groups involving in keeping soil organic carbon stability. The result will provide scientific basis for the study of biological carbon fixation in farmland ecosystems.

秸秆还田是提升潮土有机碳含量的重要途径之一，但其生物学驱动机制尚不清晰。土壤微食物网（Soil micro-food web）作为土壤生态系统重要的组成部分，参与有机碳分解和养分循环等诸多生态过程。本项目以长期秸秆还田潮土微食物网为研究对象，采用室内培养法，外源添加13C同位素标记玉米秸秆还田。采用钴60伽马射线（Co60γ）辐照法进行土壤线虫的剔除和添加试验，探讨土壤微食物网内土壤线虫和微生物的互作关系及其对土壤有机碳稳定性的作用机制，筛选提高土壤有机碳稳定性的功能团，为农田生态系统生物固碳研究提供科学依据。

外源有机碳输入是影响农田土壤有机碳动态变化的重要因素之一，在提升土壤有机质水平的同时，能够为土壤生物提供大量碳源。本研究基于室内模拟实验，重点开展了针对长期秸秆还田农田潮土，不同线虫密度、不同秸秆还田量对土壤微食物网结构及其生态功能的影响研究，通过同位素示踪技术探究外源秸秆碳在土壤微食物网不同营养级间的流动途径。主要结论如下：秸秆还田处理能够显著改变土壤微食物网的群落结构，并通过微食物网间的营养级联效应，促进食细菌线虫的生长。在土壤微食物网可承受的限度内，秸秆还田后不会影响土壤有机碳的总量，但提高了微生物碳含量，通过微生物的激发效应和食物网的续埋效应形成“以旧换新”的能力，一部分的秸秆碳会代替土壤原有的有机碳固定下来；并且这种“换新”能力与秸秆输入量密切相关，秸秆还田量越高，新生成的有机碳中来源于秸秆的组分越多。外源秸秆碳输入后土壤微食物网中同时存在“上行效应”和“下行效应”，促进了外源秸秆碳在土壤微食物网中的流动过程。该研究为探明秸秆还田土壤生态过程的生物调控机制、提升农田潮土地力提供科学依据。