Abstract:

In forest soils, bacterial communities are shaped by nutrient availability and biotic interactions. In turn, dynamics of soil bacterial communities contribute to essential soil processes involved in nutrients cycling and productivity maintaining. Knowledge of change in soil bacterial communities with forest succession process is limited. In this study, we analyzed soil bacterial community composition, structure and diversity using Illumina Miseq platform in different successional forests in Dinghushan National Nature Reserve. The successional forests included a pine forest (PF), a pine and broadleaved mixed forest (MF), and a monsoon-evergreen broadleaved forest (BF), representing early-, middle-, and advanced-successional stages, respectively, in southern China. Results showed that soil nutrient condition was improved along the successional process as indicated by the increased soil organic carbon, total nitrogen, total phosphorus, available phosphorus and soil water content from PF to BF. Proteobacteria, Actinobacteria and Acidobacteria were the dominant soil bacteria phyla in these forests. Soil bacterial community structure changed significantly along forest succession process (P<0.05). The relative abundances of Proteobacteria and Actinobacteria were relatively comparable in forests at different successional stages. The relative abundances of Acidobacteria and Planctomycetes were significantly increased from PF to BF (P<0.05), whereas that of Chloroflexi showed a decreasing tend. The abundance of k-strategy bacteria (e.g., Acidobacteria) was significantly higher in advanced-successional forest than that in early-successional forest (P<0.05), while the abundance of r-strategy bacteria (e.g., Proteobacteria) did not vary significantly in these successional forests. Soil bacteria diversity index, indicated by Shannon index, increased from early- to mid-successional forests and decreased from mid- to advanced-successional forest, resulting in the highest Shannon index in MF compared to PF and BF. Soil bacteria richness index, indicated by Chao1 index, increased from early- to advanced-successional forests. It was found that soil organic carbon, total nitrogen, soil water content, pH and nitrate were the dominant factors affecting the soil bacterial community in these successional forests. Our results suggest that soil dominant bacterial community may shift from r-strategists to k-strategists with successional process from pine forest to evergreen broadleaved forest in Dinghushan National Nature Reserve.

Key words: subtropical forests, succession, bacterial community composition, bacterial community diversity, r-strategy, k-strategy

摘要：

阐明土壤细菌群落变化对于理解土壤细菌在森林生产力维持和养分循环中的关键作用至关重要。以鼎湖山国家级自然保护区内的南亚热带地带性植被——季风常绿阔叶林及其演替阶段的马尾松林（演替初期阶段）和针阔叶混交林（演替中期阶段）为研究对象，基于Illumina Miseq测序技术，分析季风常绿阔叶林不同演替阶段森林土壤细菌群落的组成、结构和多样性。结果表明：土壤养分含量随演替的正向进行而增加，处于演替顶级阶段的季风常绿阔叶林中土壤含水量及有机碳、全氮、铵态氮、全磷和有效磷的含量均显著高于演替初期阶段的马尾松林（P<0.05）。变形菌门（Proteobacteria）、放线菌门（Actinobacteria）和酸杆菌门（Acidobacteria）为鼎湖山各演替阶段森林共有的土壤细菌群落优势门。不同演替阶段森林土壤细菌群落结构差异显著（P<0.05）。随着森林演替的正向进行，变形菌门和放线菌门的相对丰度变化不显著，但酸杆菌门和浮霉菌门（Planctomycetes）的相对丰度显著增加（P<0.05），绿弯菌门（Chloroflexi）的相对丰度呈降低趋势。适宜在稳定环境中生长的k策略细菌（如酸杆菌门）的相对丰度在演替顶级阶段显著高于初期阶段（P<0.05），而适宜在养分充足环境中快速生长繁殖的r策略细菌（如变形菌门）的相对丰度在不同演替阶段森林土壤中无显著变化。土壤细菌群落的多样性指数（Shannon指数）随着演替的正向进行呈先增加后降低的趋势，而丰富度指数（Chao 1指数）呈现逐渐增加的趋势。土壤有机碳含量、含水量、pH以及硝态氮含量的差异是导致土壤细菌群落随演替阶段发生变化的主要原因。综上所述，随着演替的进行，土壤细菌群落由r策略细菌占优势转变为k策略细菌占优势，其多样性指数和丰富度指数呈现不同的变化趋势，并且其结构和组成发生显著改变。

关键词: 亚热带森林, 演替, 细菌群落组成, 细菌群落多样性, r策略, k策略