Distinct patterns and processes of abundant and rare eukaryotic plankton communities following a reservoir cyanobacterial bloom

Abstract

Plankton communities normally consist of few abundant and many rare species, yet little is known about the ecological role of rare planktonic eukaryotes. Here we used a 18S ribosomal DNA sequencing approach to investigate the dynamics of rare planktonic eukaryotes, and to explore the co-occurrence patterns of abundant and rare eukaryotic plankton in a subtropical reservoir following a cyanobacterial bloom event. Our results showed that the bloom event significantly altered the eukaryotic plankton community composition and rare plankton diversity without affecting the diversity of abundant plankton. The similarities of both abundant and rare eukaryotic plankton subcommunities significantly declined with the increase in time-lag, but stronger temporal turnover was observed in rare taxa. Further, species turnover of both subcommunities explained a higher percentage of the community variation than species richness. Both deterministic and stochastic processes significantly influenced eukaryotic plankton community assembly, and the stochastic pattern (e.g., ecological drift) was particularly pronounced for rare taxa. Co-occurrence network analysis revealed that keystone taxa mainly belonged to rare species, which may play fundamental roles in network persistence. Importantly, covariations between rare and non-rare taxa were predominantly positive, implying multispecies cooperation might contribute to the stability and resilience of the microbial community. Overall, these findings expand current understanding of the ecological mechanisms and microbial interactions underlying plankton dynamics in changing aquatic ecosystems.

Fig. 1

Community structuring of eukaryotic plankton across bloom event. a Non-metric multidimensional scaling (NMDS) ordination of eukaryotic plankton communities based on Bray–Curtis distances. b Venn diagram showing the numbers of unique and shared OTUs between three different periods. c The pairwise Bray–Curtis dissimilarity of eukaryotic plankton communities between different periods. The top and bottom boundaries of each box indicate the 75th and 25th quartile values, respectively, and lines within each box represent the median values (n = 36). Different letters above bars indicate a significant difference at the P < 0.05 level according to nonparametric Mann-Whitney U test. All, whole eukaryotic plankton communities; Abundant, abundant plankton subcommunities; Rare, rare plankton subcommunities

Fig. 2

Time-lag regression analysis of total beta-diversity (a–c), and the turnover (green dots) and richness (red dots) components of beta-diversity (d–f) for all, abundant and rare eukaryotic plankton communities

Fig. 3

Properties of the correlation-based network. a The networks analysis showing the intra-associations within each subcommunity and inter-associations between different subcommunities. A connection stands for a strong (Spearman’s r > 0.8 or r < −0.8) and significant (P-value < 0.01) correlation. The size of each node is proportional to the number of connections (i.e., degree). Numbers outside and inside parentheses represent positive edge numbers and negative edge numbers, respectively. b–e Comparison of node-level topological features among four different subcommunities. The top and bottom boundaries of each box indicate the 75th and 25th quartile values, respectively, and lines within each box represent the median values. Different letters indicate the significant level at P < 0.05 level determined by nonparametric Mann–Whitney U test. AT abundant taxa, RT rare taxa, MT moderate taxa, CRAT conditionally rare and abundant taxa

Fig. 4

The co-occurrence patterns among OTUs revealed by network analysis. The nodes were colored according to different types of modularity classes (a) and supergroups (b), respectively. A connection stands for a strong (Spearman’s r > 0.8 or r < −0.8) and significant (P-value < 0.01) correlation. The size of each node is proportional to the number of connections (i.e., degree). Major modules have more than 40 nodes. Other modules include all small modules (n = 26) with nodes <18 per module

Fig. 5

Ternary plots showing relative abundance of OTUs from modules I–VI in the three different periods. Each circle represents one individual OTU. For each OTU, abundance was averaged over all samples at each period