典型网纹红土结构土壤细菌群落及其生态网络特征

Characteristics of Bacterial Communities and Their Co-occurrence Networks in a Typical Plinthic Horizon

我国亚热带地区均质红土剖面下部的网纹红土通常被认为是第四纪古气候和古环境变化的记录载体。迄今为止,对土壤细菌群落在土壤结构体尺度上的分异特征及其影响因素了解甚少。作为红壤关键带地下结构的重要组成部分,网纹红土独特的红–白相间的土体结构可能引起土壤细菌群落在其上的差异分布。阐明网纹红土结构土壤细菌群落特征对探索红壤关键带深部生态系统的生物多样性和多功能性具有重要的生态学意义。本研究以典型网纹红土结构体为研究对象,将其拆分为红色基质和白色网纹两部分,利用16S rRNA高通量测序分析红/白部分细菌群落与细菌生态网络的特征。结果显示,网纹结构体红白部分细菌群落组成差异显著,红色基质部分放线菌门和厚壁菌门等细菌显著富集;白色网纹部分酸杆菌门、硝化螺旋菌门等细菌的相对丰度更高。网络分析结果表明,白色网纹部分的细菌网络节点和连线较多,聚类系数较低,说明白色网纹部分细菌之间相互作用关系更复杂。典范对应分析表明,网纹结构体环境异质性造成了细菌群落组成在网纹红白部分的差异分布。其中,质地是决定细菌群落及其生态网络差异最重要的环境因子。此外,在网纹的红色基质部分,矿质养分的含量也与细菌群落的组成密切相关。

Plinthite horizon(net-like soil horizon), as a part of the Quaternary red palesols, is believed to be an important record of the Quaternary paleoclimate and paleo-environment changes of subtropical areas in China. As an important part of the subsurface structure of red soil critical zone, plinthite horizon can harbor various bacterial communities, which may play key roles in mineral weathering and soil formation processes. Previous studies usually took the entire soil layer or genetic horizon as a single sample, while the intra-horizon differentiation of bacterial communities and co-occurrence network remain largely unknown. It is hypothesed that the plinthite horizon may affect the distribution of bacterial communities in the red matrix and white veins. Clarifying the characteristics of soil bacterial communities in plinthite horizon and its impact factors would help for exploring the biodiversity and understanding the multi-functionality of red soil ecosystems. By using the high throughput sequencing processes, the plinthite structure were here divided into two parts and the bacterial communities and their ecological networks under red matrix and white veins were analyzed. Results demonstrate that there is difference of bacterial composition between red matrix and white veins. Relative abundance of the phylum of Actinobacteria and Bacteroidetes are significantly higher in the red matrix of the plinthite horizon, while the relative abundance of Acidobacteria and Nitrospirae are significantly higher in the white veins. Bacterial ecological network and its topological features are also different between the red matrix and white veins in the plinthite horizon. Co-occurrence network(CoNet) analysis demonstrate that the ecological network of white veins contains more edges and has a lower network’s clustering coefficient value. CCA analysis demonstrate that bacterial community composition and biodiversity in the plinthite horizon are caused by the environmental heterogeneity between the red matrix and white veins. Major element contents and particle size distribution are mainly impact factors that shape bacterial communities in the red matrix of the plinthite horizon.