Geographic Location Affects the Bacterial Community Composition and Diversity More than Species Identity for Tropical Tree Species

Abstract

Microorganisms associated with plants play a crucial role in their growth, development, and overall health. However, much remains unclear regarding the relative significance of tree species identity and spatial variation in shaping the distribution of plant bacterial communities across large tropical regions, as well as how these communities respond to environmental changes. In this study, we aimed to elucidate the characteristics of bacterial community composition in association with two rare and endangered tropical tree species, Dacrydium pectinatum and Vatica mangachapoi, across various geographical locations on Hainan Island. Our findings can be summarized as follows: (1) Significant differences existed in the bacterial composition between D. pectinatum and V. mangachapoi, as observed in the diversity of bacterial populations within the root endosphere. Plant host-related variables, such as nitrogen content, emerged as key drivers influencing leaf bacterial community compositions, underscoring the substantial impact of plant identity on bacterial composition. (2) Environmental factors associated with geographical locations, including temperature and soil pH, predominantly drove changes in both leaf and root-associated bacterial community compositions. These findings underscored the influence of geographical locations on shaping plant-associated bacterial communities. (3) Further analysis revealed that geographical locations exerted a greater influence than tree species identity on bacterial community compositions and diversity. Overall, our study underscores that environmental variables tied to geographical location primarily dictate changes in plant bacterial community composition. These insights contribute to our understanding of microbial biogeography in tropical regions and carry significant implications for the conservation of rare and endangered tropical trees.

Keywords: Dacrydium pectinatum; Vatica mangachapoi; bacterial composition; environmental factors; geographic location; plant identity.

Figure 1

The bacterial community compositions (class level). (A) Different plants for D. pectinatum and V. mangachapoi. (B) D. pectinatum across three locations. (C) V. mangachapoi across four locations. Abbreviation: D, D. pectinatum; V, V. mangachapoi; DL, Diaoluo; JF, Jianfeng; WZ, Wuzhi; BW, Bawang; WN, Wanning. Significance level: * p < 0.05; ** p < 0.01; *** p < 0.001.

Figure 2

Principal coordinates analysis (PCoA) of taxonomic similarity based on Bray–Curtis distances for bacterial community compositions at the OTU level. (A) Compartment and species. (B) Geographical location and species. Significance level: * p < 0.05; ** p < 0.01; *** p < 0.001. Abbreviation: loc, geographical location; com, compartment; spe, species. LE, leaf endophytic; PP, leaf epiphytic; RP, Rhizoplane; RS, Rhizosphere; RE, root endosphere.

Figure 3

Diversity of the bacterial community. (A) Accumulated OTUs (γ-diversity) for all samples in five compartments; (B) Mean OTU richness (α-diversity) of five compartments. (C) Comparison of OTU richness of five compartments of D. pectinatum and V. mangachapoi. (D) Comparison of OTU richness of D. pectinatum across five compartments in three locations. (E) Comparison of OTU richness of V. mangachapoi across four compartments in four locations. Significance level: * p < 0.05; ** p < 0.01; *** p < 0.001. “NS” means p > 0.05, not significant.

Figure 4

The relationship between environmental factors and bacterial communities in leaf and root. (A,B) Variation partitioning analysis (VPA) showing the effects of leaf and soil physicochemical properties, climate (rainfall and temperature), geographical location (latitude, longitude, and elevation), and species on bacterial community compositions (OTU level) in leaf and root. (C,D) Compositions of bacterial communities (OTU level) in leaf and roots are related to each environmental factor by partial Mantel tests. The edge width corresponds to Mantel’s r statistic for the corresponding distance correlation, while the edge color denotes the statistical significance based on 999 permutations. Significance level: * p < 0.05; ** p < 0.01; *** p < 0.001.

Figure 5

The relationship among environmental factors and the relative abundance of dominant bacterial class in leaf and root. (Only significant factors are displayed; p ≤ 0.05). (A) The relationship between environmental factors and Actinobacteria of the leaf. The dark green solid circles represent samples of D. pectinatum, and the dark brown is V. mangachapoi. The blue line and grey shade represent the fitted line and confidence interval, respectively. (B) The relationship between environmental factors and Gammaproteobacteria in leaf. The light green solid circles represent samples of Bawang, and dark green is Jianfeng. The light brown solid circles represent samples of Diaoluo, and dark brown is Wuzhi. The dark gray solid circles represent samples of Wanning. (C) The relationship between environmental factors and Actinobacteria in root. (D) The relationship between environmental factors and Acidobacteriae in root. Significance level: * p < 0.05; ** p < 0.01; *** p < 0.001.