北热带喀斯特季节性雨林土壤细菌多样性分布格局及其影响因子

Distribution pattern and influencing factors of soil bacterial diversity in the karst seasonal rainforest of northern tropics

摘要:

广西北热带喀斯特季节性雨林是我国特有的森林生态系统，然而其土壤微生物多样性及其维持机制尚不清楚。目的 探究北热带喀斯特季节性雨林土壤细菌多样性分布特征及影响因子，为该地区土壤微生物多样性及其维持机制的解析提供参考依据。方法 以弄岗北热带喀斯特季节性雨林15 hm²长期动态监测样地(以下简称弄岗样地)为例，基于16S rRNA基因高通量测序技术对其土壤细菌群落组成、多样性分布格局及其潜在影响因子进行分析。结果 弄岗样地3种生境(洼地、中坡、山顶)的土壤共包含细菌操作分类单元(operational taxonomic unit, OTU) 5 841个，隶属于35门104纲242目373科677属1 501种，主要优势细菌门为变形菌门(Proteobacteria)、放线菌门(Actinobacteriota)和酸杆菌门(Acidobacteriota)等。洼地与中坡生境的优势细菌门均为变形菌门，而山顶生境则为放线菌门。在生境水平上，土壤细菌总OTU数与特异OTU数呈洼地>中坡>山顶的规律；但在群丛水平上，尽管山顶群丛(HH)的OTU总数显著少于其他群丛，其特异OTU数量却是最多的。土壤细菌α多样性 (Chao1、Sobs、Shannon、Simpson)指数在洼地与中坡生境间差异不显著，但山顶显著低于洼地与中坡生境，群丛HH也显著低于其他群丛。β多样性主坐标分析(principal co-ordinates analysis, PCoA)表明，土壤细菌群落结构在不同生境及群丛中存在明显差异。线性判别分析(linear discriminant analysis effect size, LEfSe)表明，洼地与山顶生境的标志类群较多，而中坡的差异指示种最少。相关性分析(Spearman correlation与Mantel test)及冗余分析(redundancy analysis, RDA)表明，平均海拔(average elevation, AvELE)是影响不同生境土壤细菌分布的主要因子，土壤有机碳(soil organic carbon, SOC)、碱解氮(alkali-hydrolyzable nitrogen, AN)及速效磷(available phosphorus, AP)的影响次之。基于Tax4Fun的功能预测显示，土壤细菌群落功能在不同生境及群丛间存在显著差异，其中山顶最为特殊。结论 本研究揭示了弄岗样地土壤细菌的群落组成及其多样性分布格局，明确了海拔是影响其分布的首要因子。研究结果为解析广西北热带喀斯特季节性雨林土壤细菌多样性的维持机制提供了基础和依据。

关键词:喀斯特季节性雨林;土壤细菌;群落多样性;生境;海拔;理化因子

Abstract:

The karst seasonal rainforest of northern tropics in Guangxi is a unique forest ecosystem in China. However, the soil microbial diversity and its maintenance mechanism remain unclear.Objective This study explored the distribution characteristics and influencing factors of soil bacterial diversity in a karst seasonal rainforest of northern tropics, aiming to provide a reference for analyzing soil microbial diversity and its maintenance mechanisms in this region.Methods Soil samples were collected from a long-term dynamic monitoring plot in the karst rainforest of northern tropics (referred to as the Nonggang plot). The composition and distribution pattern of soil bacterial community were analyzed by 16S rRNA gene amplicon sequencing, and the potential influencing factors were identified by the correlation analysis.Results The soil in Nonggang plot harbored a total of 5 841 bacterial operational taxonomic units (OTUs), which were annotated to 1 501 species belonging to 677 genera, 373 families, 242 orders, 104 classes of 35 phyla. The dominant bacterial phyla were Proteobacteria, Actinobacteriota, and Acidobacteriota. The dominant bacterial phylum was Proteobacteria in both the depression and the slope habitats, and Actinobacteriota in the hilltop habitat. The number of total and specific bacterial OTUs displayed a pattern of depression>slope>hilltop habitats. The hilltop habitat association had the fewest total OTUs but the most specific OTUs. The soil bacterial alpha diversity indexes (Chao1, Sobs, Shannon, and Simpson) were not significantly different between the depression and slope habitats, while they were significantly lower in the hilltop habitat. Similarly, the hilltop habitat association had the lowest bacterial alpha diversity indexes than the other associations. The principal coordinate analysis (PCoA) of beta diversity showed differences in the bacterial communities among different habitats and associations. The linear discriminant analysis effect size (LEfSe) identified more differential groups in the depression and hilltop habitats than in the slope habitat. The Spearman correlation analysis, Mantel test and redundancy analysis (RDA) indicated that elevation was the primary factor influencing the distribution of soil bacteria in Nonggang plot, followed by soil organic carbon, available nitrogen, and available phosphorus. Tax4Fun predicted that there were significant differences in the function of soil bacterial communities among different habitats and associations, especially in the hilltop habitat.Conclusion This study revealed the community composition and diversity distribution pattern of soil bacteria in Nonggang plot and identified elevation as the primary factor affecting the distribution. These results contribute to the understanding of soil bacterial diversity and its maintaining mechanism in the karst seasonal rainforest of the northern tropics in Guangxi.

Key words:karst seasonal rainforest;soil bacteria;community diversity;habitat;elevation;physicochemical factors