基于高通量测序的连栽木麻黄根际土壤细菌群落变化研究

选取3个不同连栽代数(第一代First rotation plantation,FCP;第二代Second rotation plantation,SCP;第三代Third rotation plantation,TCP)木麻黄林地根际土壤为研究对象,通过IonS5~(TM)XL二代测序系统,从根际土壤微生物角度探究木麻黄连栽障碍形成机制。结果显示:从3个不同连栽代数木麻黄根际土壤中总共得到338560条有效序列,将其注释为17627个操作分类单元(Operational Taxonomic Units,OTUs)。α多样性指数表明,木麻黄根际土壤细菌群落的Simpson、Chao1、ACE指数随着连栽代数增加而下降,Observed species、Shannon指数呈现先增加后减少的趋势。β多样性指数表明,根际土壤中FCP与SCP之间的细菌群落多样性差异相对较大。UPGMA聚类分析结果阐明,木麻黄根际土壤FCP与SCP、TCP存在较大差异。优势细菌在属水平的热图分析结果表明,不同连栽代数木麻黄根际土壤细菌群落结构存在一定差异。随着木麻黄连栽代数增加,根际土壤中慢生根瘤菌属(Bradyrhizobium)的相对丰度呈上升趋势;与之相反,热酸菌属(Acidothermus)、根微菌属(Rhizomicrobium)、酸杆菌属(Acidibacter)、布氏杆菌属(Bryobacter)随连栽代数增加而下降;其中,与营养循环相关的有益菌属Rhizomicrobium的相对丰度随连栽代数增加而降低约311.49%、282.16%,而酸杆菌属(Acidibacter)的相对丰度随之降低约176.07%、284.54%。因此,木麻黄连栽障碍问题可能是由于根际土壤微生物群落结构失衡导致的,从而降低了森林的生态效益,使平均木生物量、林分生物量及林分净生产力下降。研究结果对揭示木麻黄连栽障碍形成的原因具有一定参考价值。

Variation of bacterial communities in the rhizosphere soils of successive rotations Casuarina equisetifolia plantations based on high-throughput sequencing analysis

Based on the IonS5^TMXL next-generation sequencing system, the rhizosphere soils sampled from three different plantations (including FCP, SCP, TCP) were used to explore the causes and mechanisms during successive rotations of Casuarina equisetifolia plantations. The results indicated that a total of 338560 effective bacterial 16S rRNA gene (V4) sequences were obtained from 3 rhizosphere soil samples, which were assigned to 17627 OTUs. Alpha diversity indices (Simpson, Chao1 and ACE) revealed that the bacterial communities in the rhizosphere soils decreased with the aggravation of successive rotations. The observed species and Shannon indices increased first and decreased afterwards. Beta diversity indices showed that the bacterial community of FCP was significantly different from that of SCP. UPGMA cluster analysis displayed that there were significant differences between FCP, SCP and TCP. Based on the heat map analysis of the dominant bacteria at the genus level, there were some differences among the structure of the bacterial communities under the successive rotations of C. equisetifolia. The relative abundance of Bradyrhizobium in rhizosphere soil increased with the increase of successive rotations. In contrast, Acidothermus, Rhizomicrobium, Acidibacter, and Bryobacter decreased with the increasing years of successive rotations. Among them, the relative abundance of Rhizomicrobium, which was related to nutrient cycling, decreased by 311.49% and 282.16%, and the Acidibacter decreased by 176.07% and 284.54%. We concluded that the consecutive monoculture problem of C. equisetifolia might be caused by the imbalance of the microbial community structure in the rhizosphere soil, thereby reducing the forest ecological benefits, and decreasing the biomass and net productivity. The results have certain significance to illustrate the reasons of consecutive monoculture problem of C. equisetifolia.