Distinct phyllosphere epiphytic and endophytic bacterial community and network structures in a tropical mangrove forest

The interactions between plants and microbes drive biodiversity maintenance, community stability and ecosystem functioning. However, differences in the community and network structures between phyllosphere epiphytic and endophytic bacteria have been less investigated. Here, we examined phyllosphere epiphytic and endophytic bacterial communities of six mangrove species using Illumina MiSeq sequencing of 16S rRNA gene. In total, 1,046 operational taxonomic units (OTUs) of epiphytic and endophytic bacteria were obtained at a 97% sequence similarity level; Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were abundant. The community composition of epiphytic and endophytic bacteria was significantly different. Plant identity significantly affected the OTU richness and community composition of both epiphytic and endophytic bacteria, with a greater effect on the community composition of epiphytic bacteria than that of endophytic bacteria. Network analysis showed that both plant-epiphytic and plant-endophytic bacterial network structures were characterized by significantly highly specialized and modular but lowly connected and anti-nested properties. Furthermore, the epiphytic bacterial network was more highly specialized and modular but less connected and more strongly anti-nested than the endophytic bacterial network. This study reveals that the phyllosphere epiphytic and endophytic bacterial communities differ and plant identity has a greater effect on the epiphytic bacteria than on endophytic bacteria. Our findings may provide a comprehensive insight into the role of plant identity in driving the phyllosphere epiphytic and endophytic microbial community structure in mangrove ecosystems.

植物与微生物的相互作用驱动着生物多样性维持、群落稳定性与生态系统功能运转。然而，目前针对叶圈（phyllosphere）附生细菌与内生细菌的群落及网络结构差异的研究仍较为匮乏。本研究针对6种红树植物的叶圈附生与内生细菌群落，通过16S核糖体RNA基因（16S rRNA gene）的Illumina MiSeq测序技术开展分析。最终在97%序列相似性阈值下，共获得附生与内生细菌的1046个操作分类单元（OTUs），其中变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）、拟杆菌门（Bacteroidetes）与放线菌门（Actinobacteria）为优势类群。附生与内生细菌的群落组成存在显著差异。植物种类对附生及内生细菌的操作分类单元丰富度与群落组成均具有显著影响，且对附生细菌群落组成的影响强于内生细菌。网络分析结果显示，植物-附生细菌与植物-内生细菌的网络结构均呈现出显著的高特化性、模块化特征，同时具备低连接度与反嵌套的属性。进一步对比发现，附生细菌网络相较于内生细菌网络，具有更高的特化性与模块化程度，连接度更低且反嵌套特性更为显著。本研究揭示了叶圈附生与内生细菌群落的差异性，且植物种类对附生细菌的影响强于内生细菌。本研究结果可为阐明植物种类在驱动红树生态系统叶圈附生与内生微生物群落结构形成中的作用提供全面的理论视角。