园林植物女贞不同生态位细菌群落结构及其多样性

Structure and diversity of bacterial community in different niches of garden plant Ligustrum lucidum Ait.

摘要:

【目的】女贞是我国分布广泛的园林绿化树种、药用植物和资源昆虫白蜡虫的优良寄主植物，解析女贞叶、茎、根、根际土壤4种生态位的细菌群落结构、物种组成和多样性特征，为研究女贞及其相关微生物组的互作及开发利用女贞内生和根际细菌资源奠定基础。【方法】以女贞叶、茎、根、根际土壤为研究材料，基于细菌16S rRNA基因V5–V7区，通过Illumina MiSeq扩增子高通量测序和生物信息学分析，比较女贞不同生态位细菌群落结构、物种组成、功能的差异性和相似性。【结果】女贞4种样本共获得168 229条有效序列，聚类后共计977个OTU，归属于23门，54纲，138目，227科和399属。不同生态位细菌群落多样性从根际土壤到根、茎、叶自下而上逐渐降低，Shannon指数分别为4.514、3.856、2.704和1.908。β-多样性分析表明，女贞4种生态位细菌群落结构存在显著差异（R=0.842 6，P<0.05），而叶与茎（R=0.481 5，P>0.05）、根与根际土壤（R=0.888 9，P>0.05）的细菌群落结构相对较为相似。在物种组成上，根、茎和叶内生细菌群落中相对丰度较高的为变形菌门和放线菌门，根际土壤中相对丰度较高的为绿弯菌门；在属水平上，女贞核心菌群主要包括红球菌属、马赛菌属、鞘氨醇单胞菌属、伯克氏菌属、慢生根瘤菌属和热酸菌属，其中伯克氏菌属、慢生根瘤菌属等为植物益生菌资源。功能预测结果显示，不同生态位细菌群落的功能以化能异养为主，地上部分（叶、茎）菌群主要在碳、氢循环中发挥作用，而地下部分（根和根际土壤）菌群主要行使与氮循环相关的功能。【结论】女贞不同生态位的细菌群落多样性自下而上呈现过滤选择机制，不同样本细菌群落结构生态位分化特征明显，在物种组成上存在植物区室特异性。女贞相关微生物群中存在多种植物益生菌，值得进一步研究和开发利用。

关键词:女贞;植物内生细菌;根际细菌;群落结构;多样性;生态位分化;功能预测

Abstract:

[Objective] Ligustrum lucidum Ait., a plant with landscaping and medical values as well as an excellent host plant for the resource insect Ericerus pela, is widely distributed in China. This study aims to investigate the community structure, species composition, and diversity of bacteria in four niches (leaf, stem, root, and rhizosphere soil) of L. lucidum, and to lay a foundation for the interaction between L. lucidum and its associated microbiota, so as to provide a scientific basis for exploiting and utilizing endophytic and rhizospheric bacterial resources. [Methods] The leaf, stem, root, and rhizosphere soil samples of L. lucidum were collected, and the V5-V7 region of bacterial 16S rRNA gene was sequenced with the Illumina MiSeq platform. The bacterial community structure, species composition, and function in different niches were compared with bioinformatics tools. [Results] The high-throughput sequencing generated 168 229 valid sequences for the four samples of L. lucidum. A total of 977 OTUs were annotated, belonging to 23 phyla, 54 classes, 138 orders, 227 families, and 399 genera. The bacterial community diversity decreased gradually in the order of rhizosphere soil, root, stem, and leaf, with the Shannon indexes of 4.514, 3.856, 2.704, and 1.908, respectively. The β-diversity analysis indicated that there were significant differences in bacterial community structure among four niches (R=0.842 6, P<0.05). The bacterial community structure was similar between leaf and stem (R=0.481 5, P>0.05) as well as between root and rhizosphere soil (R=0.888 9, P>0.05). At the level of phylum, Proteobacteria and Actinobacteriota were dominant in leaf, stem, and root, while Chloroflexi had the highest relative abundance in rhizosphere soil. The dominant genera mainly included Rhodococcus, Massilia, Sphingomonas, Burkholderia, Bradyrhizobium, and Acidothermus, some of which, like Bradyrhizobium and Burkholderia, were plant probiotics. Chemoheterotrophy was the predominant function in each niche. The bacterial community in the aboveground part (leaf and stem) mainly played a role in carbon and hydrogen cycle, while that in the underground part (root and rhizosphere soil) mainly played a role in nitrogen cycle. [Conclusion] The bacterial community diversity in different niches of L. lucidum showed a selective filtration mechanism from bottom to top. The niche differentiation of bacterial community structure was obvious in different samples, and plant compartment specificity existed in species composition. There were a variety of plant probiotics in L. lucidum-associated microbiota, which were worthy of further study and utilization.

Key words:Ligustrum lucidum Ait.;endophytic bacteria;rhizospheric bacteria;community structure;diversity;niche differentiation;function prediction