外源纤维素诱导明显影响微生物土壤结皮细菌群落结构

Induction effect of exogenous cellulose on bacterial community of microbial soil crust

摘要:

【目的】微生物土壤结皮(Microbial soil crusts, MSCs)对于遏制土壤荒漠化、恢复荒漠地区生态环境起着重要作用。MSCs中的微生物, 特别是纤维素降解菌, 起着稳固、修复生态环境的功能。外源纤维素诱导是全面认识MSCs中纤维素降解细菌的多样性及其在MSCs形成和发展中的作用的重要途径。【方法】通过对微生物土壤结皮分别添加小麦秸杆(麦秸)、锯末木屑两类纤维素材料进行诱导, 以PCR-DGGE方法分析细菌群落变化。【结果】外源纤维素, 特别是麦秸的添加会迅速提高MSCs中细菌丰富度及多样性, 将细菌丰富度提高约66.7%, Shannon-Weiner指数提高约15.8%; 相同处理的样品聚类位置较近, 说明纤维素对于MSCs细菌菌群变化起主导作用; 细菌群落结构组成在添加纤维素诱导后发生了变化, 麦秸诱导样品与同时期对照样品差异最大, 但各样品中Firmieutes和Alphaproteobacteria始终为优势类群; 所得DGGE条带序列中有13条与纤维素降解菌序列同源性相近, 他们所代表的细菌很可能具有纤维素降解能力, 其中厌氧性的梭菌属(Clostridium)所占比例最大, 约为46.1%, 其次为芽孢杆菌属(Bacillus), 约占30%; 纤维素降解过程中, 诱导增加了MSCs发育有重要作用的一些类群如Microcoleus vaginatus和一些Alphaproteobacteria类群细菌等的丰度和多样性, 它们中有的可通过分泌多糖物质等增强土壤颗粒黏结、有的可以其固碳或固氮等能力提高土壤营养水平。【结论】为认识外源纤维素诱导MSCs细菌群落结构的变化规律, MSCs中纤维素降解细菌的多样性及纤维素降解细菌对MSCs形成和发展的作用提供了基础, 同时也为恢复荒漠生态系统实践方法提供了理论依据。

Abstract:

[Objective] Microbial soil crusts (MSCs) play an important role in the restoration of the ecological environment and the containment of soil desertification. The microbes in MSCs, especially the cellulose degrading bacteria (CDB), can stablize and repair the related ecological environment. The induction of exogenous cellulose is a major pathway for the full acknowledgment in the CDB’s diversity and their contribution to MSCs’ development. [Methods] Two cellulose materials (crushed wheat straw and sawdust) were added into MSCs separately, to determine the variation of the bacterial community induced by the exogenous cellulose based on PCR-DGGE. [Results] The exogenous cellulose especially wheat straw, rapidly increased the diversity and richness of bacterial community by approximately 66.7% and 15.8%, respectively. Samples subjected to the same treatment well grouped in together in cluster analysis based on DGGE bands profiles, suggesting that cellulose has a crucial effect on the bacterial community. The exogenous cellulose induced a remarkable variation of the structure of the bacterial community, of which the most variable was caused by wheat straw. Firmieutes and Alphaproteobacteria groups were always the predominant group in all samples. Among the obtained sequences, 13 bands were closely and phylogeneticly related to CDB and therefore they may be sourced from CDB. The anaerobic Clostridium group predominated these possible CDB (accounted for 46.1%), followed by Bacillus (30%). The exogenous cellulose degradation also induced the increase of the abundance or richness of some specific bacteria, like Microcoleus vaginatus and some Alphaproteobacteria groups, which had a significant function in MSCs development with the abilities in secreting polysaccharides to enhance the cohesion of soil particles or fixing carbon and/or nitrogen to improve the soil nutrition level. [Conclusion] Results provided a basis for the appreciation of the CDB diversity and the variation of the bacterial community structure induced by exogenous cellulose, and meanwhile lent theory evidence for the practical pathway in desert ecosystem restoration.