泰山4种优势造林树种细根分解对细菌群落结构的影响

Effects of fine root decomposition on bacterial community structure of four dominated tree species in Mount Taishan,China

为了理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响,该研究以泰山4种主要优势造林树种刺槐(Robinia pseudoacacia)、麻栎(Quercus acutissima)、油松(Pinus tabulaeformis)和赤松(Pinus densiflora)为研究对象,采用凋落物分解袋法及IlluminaMiseq测序平台对细菌16SrDNAV4–V5区扩增产物进行双端测序,分析了4种树种细根分解对细菌群落结构及多样性的影响。结果表明:(1) 4种植物细根分解速率差异显著,阔叶树种分解速率显著高于针叶树种,表现为刺槐>麻栎>油松>赤松。(2)4个树种细菌序列操作分类单元(OTU)、观测到的物种数、Ace指数和系统发育多样性之间差异显著,且阔叶树种刺槐和麻栎显著低于针叶树种赤松和油松。4种细根分解的细菌群落结构存在极显著差异。细根初始碳(C)含量、木质素:氮(N)和C:N对细菌群落结构的影响较大。(3)细菌群落相对丰度在5%以上的优势类群是变形菌门、放线菌门、拟杆菌门、酸杆菌门,且变形菌门、酸杆菌门在4个树种之间差异显著,特别是阔叶树种变形菌门显著高于针叶树种。在纲水平上,α-变形菌纲、β-变形菌纲、γ-变形菌纲、不明放线菌纲、鞘脂杆菌纲为主要的优势纲,其中α-变形菌纲、不明放线菌纲在4个树种之间差异显著。(4) Pearson相关性分析表明,细菌优势门和纲相对丰度受到凋落物初始化学性质的影响,特别是变形菌门和α-变形菌纲;变形菌门和α-变形菌纲相对丰度与细根分解速率显著正相关。冗余分析结果也显示,细根初始N、磷(P)含量和木质素含量对细菌群落结构的影响较大。研究结果有助于理解细菌群落结构和多样性对森林生态系统细根凋落物分解的影响。

Aims Microorganisms play a crucial role in the litter decomposition process in terrestrial ecosystems.Understanding the independent and interactive relationship between fine root decomposition and bacteria community related to substrate characteristics can help to predict the consequences of changes on ecosystem function.Therefore,the aim of this study was to identify fine roots’influences on rhizosphere microbial structure and diversity.Methods The decomposition of root litters of four dominant tree species of Mount Taishan(Robinia pseudoacacia(RP),Quercus acutissima(QA),Pinus tabulaeformis(PT)and Pinus densiflora(PD))was tested in a Yaoxiang Forest Farm.Using Illumina high-throughput sequencing of 16S rRNA genes,bacterial community composition was determined.Composition,diversity and relative abundance of bacteria were calculated for per fine root litter.Important findings(1)Fine root litter decomposition differed significantly among different root types.There was no difference in decomposition rate between broad-leaved species and conifer species.In all species,fine roots of RP and QA were more strongly decomposed than that of PT and PD,and these differences were significant(RP>QA>PT>PD).(2)The number of observed species,operational taxonomic units,Ace index and phylogenetic diversity in broad-leaved species were significantly lower than that in coniferous species.Bacterial community structure differed significantly among four species for root decomposition.Initial carbon(C),lignin:nitrogen(N)and C:N in fine root had a great influence on the bacterial community structure.(3)At the phylum level,a total of 4 phyla were dominant(>5%across all species).Based on the average relative abundance,the most abundant phyla were Proteobacteria,Actinomyces,Bacteroidetes and Acidobacteria.Proteobacteria’s and Acidbacteria’s abundance were significantly different among the four species.Particularly,the Proteobacteria of broad-leaved species was significantly higher than that of coniferous species.At the class level,a wide range of classes dominated.Based on the average relative abundance,the most abundance classes were Alphaproteobacteria,Betaproteobacteria,Gammaproteobacteria,unidentified-Actinobacteria and Sphingobacteriia.Alphaproteobacteria and unidentified-Actinobacteria had significant differences among the four species.(4)Pearson correlation analysis showed that the relative abundance of dominant phylum and class was affected by the initial properties of root litter,especially the Proteobacteria and Alphaproteobacteria.In addition,there was a significant positive correlation between fine root decomposition rate and relative abundance of Proteobacteria and Alphaproteobacteria.Redundancy analysis(RDA)also demonstrated that the initial properties of fine root litter(initial N,P,C:N)had significant effects on the structures of bacterial community.These results can improve understanding the links between fine root litter decomposition and functional microbial communities.