Structure and diversity of hypolithic diazotroph in central gobi

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.