不同时间尺度下蚯蚓对农田土壤微生物群落的影响

Sustainable agriculture needs the self-organized soil functions driven by biological interactions. Although the potentials of earthworm as a beneficial organism in regulating soil ecosystem functions have been well-known in terms of theoretical and practical views, the effects of geophagous earthworm on soil microbial community in agroecosystem have been neglected and not mechanically understood yet so far. In particular, neither are there studies simultaneously analyzing prokaryotes and micro-eukaryotes nor studies do systematically concern the effects of earthworms from gut, cast to bulk soil, i.e. a complete process reflecting the earthworm effects on soil. Moreover, there are shortage of attempts to integrate various temporal and spatial scales to elucidate the earthworm effects. With the long-term in situ field experiment, the in situ field investigation and laboratory incubation, the current project would comprehensively assess short-term/long-term and direct/indirect effects of microbial community by the indigenous Metaphire guillelmi via the techniques such as high throughout sequencing and functional microarray. Following the dynamic patterns of soil microbial community from earthworm gut to cast and bulk soil, the direct and indirect factors or mechanisms inherently driving soil microbial community by earthworm would be explored and disentangled. Taken together, our results will not only help clarify the mechanisms of soil fauna on microbial community, it also guide future management to manipulate soil biota or to utilize the valuable biological resources for the development of sustainable agriculture.

可持续农业需要发挥土壤生物相互作用的自组织功能。虽然蚯蚓作为有益生物在调控土壤生态功能上的潜力和应用价值已得到公认，但迄今有关食土型蚯蚓对微生物群落影响及机制的认识仍刚刚起步，如缺乏对土壤原核和真核生物的全面分析，忽视从肠道、蚓粪到田间土壤的系统研究，尤其是缺少考虑蚯蚓影响的时空尺度因素。本项目借助蚯蚓接种农田长期定位试验、野外原位调查采样及室内调控培养试验，利用高通量和功能基因芯片技术系统评估了蚯蚓对土壤微生物群落结构的长期/短期及直接/间接影响；在此基础上，以蚯蚓肠道、蚓粪及蚯蚓长期作用下的土壤为对象，着重研究蚯蚓对土壤微生物群落的直接和间接影响因素及机制。预期结果不仅可深化有关土壤动物对微生物影响机制的认识，而且为今后将有益生物资源及调控土壤生物功能纳入可持续管理体系奠定基础。

虽然蚯蚓作为有益生物在调控土壤生态功能上的潜力和应用价值已得到公认，但迄今有关食土型蚯蚓对微生物群落影响及机制的认识仍刚刚起步。本项目结合蚯蚓接种农田长期定位试验、野外原位调查采样及室内调控培养试验，针对土壤原核和真核生物的全面分析，从肠道、蚓粪到田间土壤的不同时空尺度进行了系统研究，利用分子分析技术系统评估了蚯蚓对土壤微生物群落组成和结构的长期/短期及直接/间接影响。结果表明：（1）与无蚯蚓的对照相比，蚓粪中纤毛虫数量显著下降，鞭毛虫数量在蚓粪中最高并显著高于穴壁。食细菌类原生生物为蚯蚓介导的各微域内优势功能群，穴壁和蚓粪中寄生类原生生物相对丰度高于无蚯蚓的对照。蚯蚓种类与微域类型对土壤原生生物多样性有显著的交互影响，并受采样时间的影响。蚯蚓改变了土壤原生生物与细菌间的生态网络关系。不同蚯蚓、不同微域类型的网络共现性、模块化系数、关键原生生物种不同，表明以土壤原生生物为核心的微生物群落的复杂程度依赖于蚯蚓的种类与微域类型。（2）不论氮输入量如何，蚯蚓肠道内容物中土壤鞭毛虫、纤毛虫、变形虫数量，自养类、寄生类、食细菌类原生生物相对丰度显著降低；与未被蚯蚓取食的土壤和蚓粪相比，蚯蚓肠道内容物中土壤原生生物多样性显著降低；同时伴随氮水平增加，未被蚯蚓取食的土壤与蚓粪中，原生生物香农多样性无显著差异，OTU丰度呈现下降趋势。蚯蚓取食前后，土壤原生生物群落与细菌的生态网络关系发生变化。与未被蚯蚓取食的土壤和蚓粪相比，肠道内容物中原生生物节点数显著下降，网络平均度下降。（3）蚯蚓的活动整体增加了根际土壤微生物碳作为短期周转碳库的含量，改变微生物群落结构从而会导致土壤碳的损失。在高质量凋落物土壤氮资源丰富时，蚯蚓提高微生物活性，最终导致土壤碳损失。本项目的结果深化了蚯蚓对土壤微生物群落影响机制的认识，为今后将利用有益生物资源调控土壤生物功能奠定了基础。