镉积累对艾纳香内生菌群落结构和共发生网络的影响

Effects of cadmium accumulation on the structure and co-occurrence network of endophytic bacterial community in Blumea balsamifera

为探究器官镉(Cd)积累对艾纳香内生菌的影响,该文采用16S rRNA基因高通量测序技术结合分子生态网络分析,研究不同外源镉处理(0、2.0 mg·kg^(-1))下艾纳香根、茎、叶Cd积累对内生菌群落结构特征的影响。结果表明:(1)与未添加外源Cd(0 mg·kg^(-1),Cd0)相比,Cd(2.0 mg·kg^(-1),Cd2)处理促进了植株生长,根、茎、叶中Cd积累量顺序为叶(16.75 mg·kg^(-1))>茎(11.99 mg·kg^(-1))>根(3.96 mg·kg^(-1))。(2)α多样性分析表明,各器官内生菌丰富度(Sobs指数、Ace指数和Chao1指数)和多样性(Shannon指数和Simpson指数)均以根最高,茎次之,叶最低,并且Cd2处理各器官内生菌丰富度和多样性均高于Cd0处理。(3)在门水平上,两个处理根、茎、叶内生菌均以变形菌门、放线菌门和厚壁菌门为优势菌群;在属水平上,代尔夫特菌是Cd0和Cd2处理各器官的主要菌属,相对丰度分别为53.0%~92.7%和57.1%~89.2%;艾纳香根、茎、叶内生菌群落结构有一定的相似性,Cd2处理提高了根、茎、叶共有内生菌属的比例及各器官(根除外)独有内生菌属比例。(4)线性判别分析(LEfSe)表明,相同处理不同器官间及不同处理相同器官间内生菌属存在差异。(5)冗余分析(RDA)发现,根际土壤Cd含量、器官Cd含量与内生菌群落结构组成有明显的相关性。(6)共发生网络分析结果显示,Cd积累使艾纳香根、叶内生菌共发生网络变得复杂且增强了根、茎物种间的竞争作用和叶物种间的协同共生作用。综上认为,外源Cd处理影响了艾纳香各器官内生菌群落结构及相互作用模式。

To probe into the impacts of organ cadmium accumulation on endophytic bacteria in Blumea balsamifera,the methods of high-throughput sequencing of 16S rRNA gene V3-V4 region and molecular ecological network analysis were employed to study the effects of Cd accumulation in root,stem and leaf of B.balsamifera on the community characteristics of endophytic bacteria under different exogenous cadmium treatments(0 and 2.0 mg·kg^(-1)).The results were as follows:(1)In comparison with the control group without exogenous cadmium addition(0 mg·kg^(-1),Cd0),the treatment group with cadmium spiking(2.0 mg·kg^(-1),Cd2)in soils promoted plant growth and the cumulative Cd contents in root,stem and leaf,with the order of leaf(16.75 mg·kg^(-1))>stem(11.99 mg·kg^(-1))>root(3.96 mg·kg^(-1)).(2)αdiversity analysis showed that the endophytic bacteria richness(Sobs,Ace and Chao1 indices)and diversity(Shannon and Simpson indices)for organs were the highest in root,followed by stem and leaf under Cd0 and Cd2 treatments.Additionally,the indices of richness and diversity of endophytic bacteria for each organ under Cd2 treatment were superior to those under Cd0.(3)At the phylum level,Proteobacteria,Actinobacteriota and Firmicutes were the dominant bacterial phyla in all the organs for both treatments;at the genus level,Delftia was the main bacterial genus with the relative abundance ranged from 53.0%to 92.7%and 57.1%to 89.2%in the plant organs of Cd0 and Cd2,respectively;certain similarities existed among the endophytic bacterial community structures of root,stem and leaf of B.balsamifera,and Cd2 increased the proportion of mutual endophytic bacterial genera in root,stem and leaf and that of unique endophytic ones in each organ(except for the root).(4)Linear discriminant analysis Effect Size(LEfSe)analysis showed that there existed the differences on endophytic bacterial genera residing in different organs within the same treatment and also the same organ between treatments.(5)Redundancy analysis(RDA)showed that the contents of rhizosphere soil Cd and plant organ Cd were significantly correlated with the composition of endophytic bacterial community.(6)Co-occurrence network analysis clarified that cadmium accumulation in B.balsamifera complicated the interaction network of endophytic bacteria occurring in root and leaf,and enhanced the competition among endophytic bacterial species in root and stem,and the symbiosis in leaf.In summary,exogenous Cd treatment affected the community structure and interaction mode of endophytic bacteria in B.balsamifera organs.