Date Published: April 5, 2017
Publisher: Public Library of Science
Author(s): Zhiwen Wei, Xiaolong Hu, Xunhang Li, Yanzhou Zhang, Leichun Jiang, Jing Li, Zhengbing Guan, Yujie Cai, Xiangru Liao, A. Mark Ibekwe.
Soil bacteria are important drivers of biogeochemical cycles and participate in many nutrient transformations in the soil. Meanwhile, bacterial diversity and community composition are related to soil physic-chemical properties and vegetation factors. However, how the soil and vegetation factors affect the diversity and community composition of bacteria is poorly understood, especially for bacteria associated with evergreen and deciduous trees in subtropical forest ecosystems. In the present paper, the microbial communities of rhizospheric soils associated with different types of trees were analyzed by Illumina MiSeq sequencing the V3-V4 region of the 16S rRNA gene. A total of 121,219 effective 16S rRNA gene sequences were obtained, which were classified into 29 bacterial phyla and 2 archaeal phyla. The dominant phyla across all samples (>5% of good-quality sequences in each sample) were Proteobacteria, Acidobacteria, Firmicutes and Bacteroidetes. The bacterial community composition and diversity were largely affected by both soil pH and tree species. The soil pH was the key factor influencing bacterial diversity, with lower pH associated with less diverse communities. Meanwhile, the contents of NO3− were higher in evergreen tree soils than those associated with deciduous trees, while less NH4+ than those associated with deciduous trees, leading to a lower pH and indirectly influencing the diversity and composition of the bacteria. The co-occurrence patterns were assessed by network analysis. A total of 415 pairs of significant and robust correlations (co-occurrence and negative) were identified from 89 genera. Sixteen hubs of co-occurrence patterns, mainly under the phyla Acidobacteria, Proteobacteria, Firmicutes and Bacteroidetes, may play important roles in sustaining the stability of the rhizospheric microbial communities. In general, our results suggested that local environmental conditions and soil pH were important in shaping the bacterial community of the Taihu Lake zone in east China.
Soil, especially the rhizosphere of plants, is a complex and heterogeneous environment inhabited by various microorganisms. The interactions of plant roots and microorganisms are important for the plant performance as well as ecosystem functioning . It is well known that soil microbes serve as a major reservoir of nutrients for plants through their active involvement in nutrient cycling through organic matter degradation , nitrogen cycling and mineral weathering [3, 4], which affect plant growth . Similarly, the functional and taxonomic diversity of rhizospheric microbial communities are strongly influenced by biotic and/or abiotic factors, such as root exudates, competition for nutrients, edaphic characteristics and climate modifications [6–9]. Root exudates are affected by the plant species and genotype , including a wide range of compounds, such as amino acids, sugars, enzymes and siderophores , which can largely affect the structure of the rhizospheric microbial community and reinforce the activity of microbial communities . While, most of this knowledge has come from cultivation-dependent approaches, yielding only a partial understanding of the interactions among microbes, plants and soil. In fact, cultivation-independent methods for determining microbial communities have suggested that cultivated isolates represent less than 1% of the bacterial taxa .