中央戈壁石下生物土壤结皮固氮细菌群落结构和多样性

Structure and diversity of hypolithic diazotroph in central gobi

摘要:

【背景】戈壁荒漠石下生物土壤结皮(Biological Soil Crusts，BSCs)由石下生物定殖繁衍而成，广泛存在于石英石下方，在相关生态系统的物质循环中起重要作用；其细菌群落结构受空间和土壤环境因子影响而变化较大。固氮细菌是石下BSCs的形成和发育主要驱动力；中央戈壁面积较大，为温带的代表戈壁之一，但目前其石下BSCs中固氮细菌群落结构和多样性尚未有研究报道。【目的】阐释中央戈壁石下BSCs中固氮细菌的群落结构、多样性及其影响因素。【方法】应用MiSeq对nif H基因进行高通量测序，并使用生物信息学方法基于nif H序列分析固氮细菌的群落结构和多样性及其影响因素。使用CoNet软件绘制物种共现性图，以期揭示石下固氮细菌群落结构的关键物种。【结果】石下固氮细菌的优势菌门有Cyanobacteria (47.20%?69.90%)和Proteobacteria (27.47%?48.91%)；优势菌属为Scytonema (45.05%?69.09%)、Skermanella (10.26%?20.48%)和未知属(13.72%?22.00%)；9月份物种丰富度较5月份高，但这2个月份的多样性无明显差异；在土壤理化因子中，速效氮对石下固氮细菌群落组成的影响最大；其中各微生物之间均存在较强的互作关系，以共存关系为主(约占66.98%)，点度中心性、接近中心性和中介中心性均较高的节点属于alphaproteobacteria。【结论】中央戈壁石下BSCs中固氮细菌以Cyanobacteria和Proteobacteria为最优势菌群；alphaproteobacteria为稳定石下BSCs固氮细菌群落的关键类群，可能是主要固氮者，这为认识和利用石下生物土壤结皮固氮细菌提供了基础依据。

Abstract:

[Background] Hypolithic biological soil crusts (BSCs) in the Gobi desert are colonized and multiplied by under-rock organisms, widely exist under quartzite, and play an important role in the material cycle of related ecosystems. The bacterial community structure was greatly shifted with the change of spaces and different type of soils. Nitrogen-fixing bacteria are the main driving force for the formation and development of hypolithic BSCs. The central gobi has a wide area and as a representative of the temperate gobi. However, there are no research reports on the community structure and diversity of nitrogen-fixing bacteria in hypolithic BSCs. [Objective] To explain the community structure, diversity and factors influencing nitrogen-fixing bacteria in hypolithic BSCs. [Methods] The methods included Miseq to perform high-throughput sequencing of the nifH gene; bioinformatics to analyze the community structure and diversity of nitrogen-fixing bacteria and its influencing factors based on the nifH sequence, and CoNet software to map species co-occurrence networks to discover key species. [Results] In hypolithic BSCs, the dominant phyla were Cyanobacteria (47.20%?69.90%) and Proteobacteria (27.47%?48.91%), and genera were Scytonema (45.05%?69.09%), Skermanella (10.26%?20.48%) and unclassified genera (13.72%?22.00%). The species richness in September was higher than that in May, but there was no significant difference between the two months. Among others, available nitrogen was the soil physical and chemical factor that had the greatest impact on the composition of nitrogen-fixing bacterial communities in the hypolithic BSCs. There was a strong interaction between the microorganisms in nitrogen-fixing bacteria under the rock, and the relationship was mainly coexistence (about 66.98%). In the CoNet network, the nodes with high degree of centrality, close centrality and betweenness centrality all belonging to alphaproteobacteria. [Conclusion] Cyanobacteria and Proteobacteria were the most dominant nitrogen-fixing bacteria in hypolithic BSCs of Central Gobi. alphaproteobacteria was the key species stabilizing the nitrogen-fixing bacterial community and may be the main nitrogen fixers. This study provided a basic basis for understanding and using the nitrogen-fixing bacteria associated with hypolithic BSCs.