Deterministic processes dominate archaeal community assembly from the Pearl River to the northern South China Sea

Abstract

Archaea play a significant role in the biogeochemical cycling of nutrients in estuaries. However, comprehensive researches about their assembly processes remain notably insufficient. In this study, we systematically examined archaeal community dynamics distinguished between low-salinity and high-salinity groups in water and surface sediments over a 600-kilometer range from the upper Pearl River (PR) to the northern South China Sea (NSCS). Neutral community model analysis together with null model analysis showed that their C-score values were greater than 2, suggesting that deterministic processes could dominate the assembly of those planktonic or benthic archaeal communities at both the low-salinity and high-salinity sites. And deterministic processes contributed more in the low-salinity than high-salinity environments from the PR to the NSCS. Furthermore, through the co-occurrence network analysis, we found that the archaeal communities in the low-salinity groups possessed closer interactions and higher proportions of negative interactions than those in the high-salinity groups, which might be due to the larger environmental heterogeneities reflected by the nutrient concentrations of those low-salinity samples. Collectively, our work systematically investigated the composition and co-occurrence networks of archaeal communities in water as well as sediments from the PR to the NSCS, yielding new insights into the estuary's archaeal community assembly mechanisms.

Keywords: archaeal community; co-occurrence network; deterministic processes; neutral community model; null model; stochastic processes.

Figure 1

Sampling stations from the Pearl River to the northern south China Sea. Inset, enlarged views of part of the studied areas; blue dots, sampling stations.

Figure 2

Archaeal community composition at the phylum level (A) and genus level (B) based on 16S rRNA gene.

Figure 3

Fit of the neutral community model (NCM) of community assembly for all water, all sediment, the high-salinity-water, low-salinity-water, high-salinity-sediment, and low-salinity-sediment groups samples from the Pearl River to the northern South China sea region. The solid blue lines indicate the best fit to the neutral community model (NCM), and the dashed blue lines represent 95% confidence intervals around the NCM prediction. OTUs that occur more or less frequently than predicted by the NCM are shown in green and red, respectively. m indicates the immigration rate, R² indicates the fit to this model.

Figure 4

Co-occurrence networks of the archaeal community in the high-salinity-water (A), low-salinity-water (B), high-salinity-sediment (C), and low-salinity-sediment (D) groups based on pairwise Spearman’s correlations between OTUs. Each shown connection has a correlation coefficient|r| > 0.6 and a p value <0.05. The red edges represent significant positive correlations, and the blue edges represent significant negative correlations. The size of each node is proportional to the number of connections, and each node was colored by modularity.

Figure 5

C-score metric using null models. The values of observed C-score (C-score_obs) > simulated C-score (C-score_sim) indicate non-random co-occurrence patterns. Standardized effect size (SES) < −2 and > 2 represents aggregation and segregation, respectively.