Similar but different assembly processes of bacterial and micro-eukaryotic communities in an urban river

Abstract

Bacteria and micro-eukaryotes play important roles in river ecological systems. The processes that govern bacterial and micro-eukaryotic communities in urban rivers are still uncertain. The spatiotemporal characteristics and assembly processes of bacterial and micro-eukaryotic communities in the Xiangjianghe River were explored using 16 S and 18 S rRNA gene amplicon sequencing in the present study. The results indicate that the bacterial and micro-eukaryotic community composition exhibited distinct temporal and spatial variation. The topological characteristics of co-occurrence networks demonstrate that the bacterial and micro-eukaryotic community coexistence patterns vary significantly between the four seasons. Water temperature (WT) and oxidation-reduction potential (ORP) were detected as the most critical factors affecting bacterial and micro-eukaryotic community structure. The stochastic process (dispersal limitation) was the dominant assembly process for bacteria and micro-eukaryotes in all seasons. Deterministic and stochastic processes influenced the bacteria and micro-eukaryotes differently. Compared to bacteria, the values of niche breadth were relatively lower, and the proportion of deterministic processes was relatively higher in micro-eukaryotes. These results expand our understanding of spatiotemporal patterns, assembly mechanisms, and influencing factors of bacterial and micro-eukaryotic communities in urban rivers.

Keywords: Bacteria; Community assembly; Micro-eukaryotes; Seasonal variation; Stochastic process.

Fig. 1

Location of the sampling sites in the Xiangjianghe River.

Fig. 2

Alpha diversity of bacterial and micro-eukaryotic communities. *, **, and *** represent p < 0.05, p < 0.01, and p < 0.001, respectively. Different letters above the bar chart indicate significant differences between sampling sites (p < 0.05).

Fig. 3

Seasonal variation of bacterial and micro-eukaryotic community composition in the XJH. Venn diagram displaying the OTUs richness distribution of bacteria (a) and micro-eukaryotes (b) in different seasons. Nonmetric multidimensional scaling analysis (NMDS) of bacterial (c) and micro-eukaryotic (d) community at OTU level based on Bray-Curtis distance in different seasons. Mean relative abundance of different phyla at different sampling sites in four seasons for bacteria (e) and micro-eukaryotes (f). Significance test of the difference in the relative bacterial (g) and micro-eukaryotic (h) abundance at the phylum level among four seasons using the Kruskal-Wallis H test.

Fig. 4

Co-occurrence networks of bacterial and micro-eukaryotic communities in different seasons (a), and keystone species analysis based on Zi-Pi plots for bacteria (b) and micro-eukaryotes (c).

Fig. 5

Environmental factors affecting microbial community. (a) Environmental drivers of the bacterial and micro-eukaryotic communities by Mantel test; (b) Correlation of top 10 abundant phyla to environmental factors in bacteria; (c) Correlation of top 10 abundant phyla to environmental factors in micro-eukaryotes. *, **, and *** represent p < 0.05, p < 0.01, and p < 0.001, respectively.

Fig. 6

Assembly process of the microbial community in different seasons. (a) Fit of the neutral community model (NCM) of bacteria and micro-eukaryotes in four seasons. Green and red dots represent the OTUs occurred more and less frequently than predicted, respectively. The black solid line represents the best fit to the NCM and the black dashed lines indicate the 95% confidence interval. (b) Relative contributions of different ecological processes in assembling the bacterial and micro-eukaryotic community. (c) Levins’ niche breadth of bacterial and micro-eukaryotic in four seasons. Different letters represent significant differences among the four seasons (p < 0.01, multiple comparisons after the Kruskal-Wallis test).