Bihong Liu

Marine fungi are pivotal components of coastal ecosystems, facilitating essential biogeochemical cycling and trophic dynamics. However, the complex mechanisms governing their spatiotemporal community patterns in tropical–subtropical coasts remain largely unexplored. In this study, we characterized marine fungal diversity across a comprehensive seasonal cycle (spring (March), summer (June), autumn (August), and winter (December)) at 21 representative sites along the Leizhou Peninsula, China. These sites were strategically selected to encompass a broad range of dissolved inorganic nitrogen (DIN) gradients. Fungal community composition was characterized via high-throughput sequencing of the internal transcribed spacer 2 (ITS2) region, followed by functional guild profiling using the FUNGuild database. A total of 8777 amplicon sequence variants (ASVs) were identified, encompassing a broad taxonomic breadth of 10 phyla and 358 genera. Ascomycota, Basidiomycota, and Chytridiomycota emerged as the predominant phyla across all samples. Our results revealed significant spatiotemporal heterogeneities: seasonal succession fundamentally reshaped community composition, with DIN exerting its most pronounced influence during the winter. Furthermore, fungal functional structures exhibited distinctive clustering across regions defined by DIN enrichment levels. Co-occurrence network analysis revealed a highly modular and robust architecture, characterized by predominantly positive interactions and dense inter-taxon connectivity. These findings underscore the synergistic influence of temporal dynamics and DIN enrichment in shaping marine fungal community assembly and functional compositions. Our study provides critical baseline insights into the ecological resilience of coastal mycobiota in the South China Sea.

To investigate the seasonal dynamics of phytoplankton community structure and its relationship with environmental factors in the coastal waters of the Leizhou Peninsula, China, surveys were conducted at 21 stations during four seasonal cruises: autumn (August 2022), winter (December 2022), spring (March 2023), and summer (June 2023). A total of 174 phytoplankton species from 7 phyla were identified. Species richness peaked in summer (93 species, 5 phyla), followed by winter (80 species, 3 phyla), spring (79 species, 5 phyla), and autumn (75 species, 5 phyla). Bacillariophyta dominated throughout the year, with Skeletonema costatum (Greville) Cleve 1878 and Chaetoceros lorenzianus Grunow 1863 being consistently dominant across all seasons. Phytoplankton cell density showed a distinct seasonal pattern, highest in autumn, followed by summer, and lower in spring and winter. Diversity indices (H, J, D) indicated moderately to heavily polluted waters. Redundancy analysis identified salinity, dissolved inorganic nitrogen, chlorophyll a (Chl a), pH, water temperature, chemical oxygen demand, and dissolved silicon as key environmental drivers, with their influence varying seasonally: salinity was strongest in summer, Chl a in winter, and multiple factors jointly shaped the community in spring and autumn. This study provides a comprehensive assessment of phytoplankton biodiversity and clarifies the environmental drivers of their distribution in the coastal waters of the Leizhou Peninsula, China.

Fungi are one of the major components of the eukaryotic microbial community in marine ecosystems, playing a significant role in organic matter cycling and food web dynamics. However, the diversity and roles of fungi in marine sediments remain poorly documented. To elucidate the diversity and spatial distribution of fungal communities in the marine sediments of an estuary–coast continuum across three distinct salinity regions in Zhanjiang Bay, China, the variations in fungal diversity, abundance, community structure, and distribution in the sediments were investigated through the application of high-throughput amplicon sequencing using the internal transcribed spacer (ITS) primers. Additionally, the FUNGuild database was employed to assess the potential functional traits of fungi. A total of 1242 ASV sequences, affiliated to 144 genera and five phyla, were identified. Ascomycota (68.97%) and Basidiomycota (6.41%) were the dominant fungal groups, together accounting for 75.38% of the total relative abundance of the fungal community. Significant differences were observed in the α-diversity indices (Shannon index and richness) and β-diversity of fungal communities across the three distinct salinity regions. The fungal molecular network exhibited primarily positive species interactions, with notable structural differences across salinity gradients. The low-salinity group had a large network with high modularity; the medium-salinity group a small, simple network with high centralization, and the high-salinity group a compact, moderately complex network. Symbiotrophs, saprotrophs, and pathotrophs, being the three trophic types with the highest proportions, were estimated based on ITS. A redundancy analysis (RDA) indicated that salinity was the primary factor influencing the distribution of Ascomycota communities, while the distributions of Basidiomycota, Chytridiomycota, Mucoromycota, and Rozellomycota were more strongly affected by environmental factors such as chlorophyll a, chemical oxygen demand (COD), pH, and temperature. Our work provides new scientific data on the diversity, composition, and distribution of fungal communities in Zhanjiang Bay, which helps to understand the biodiversity of fungi in the estuary–coast ecosystems.

In order to investigate the effects of various nitrogen (ammonium) concentrations on the epibiotic bacterial community associated with Oocystis borgei, a metabarcoding sequencing method was employed. The 16S rDNA sequencing and bioinformatic analysis were conducted on cultures of O. borgei that were grown on four different nitrogen element concentrations (2.5, 10, 50, and 100 mg/L), and the differences in the epibiotic bacterial community and functions of O. borgei among different nitrogen concentrations were compared. The results showed that the chlorophyll a content of O. borgei increased with increasing nitrogen concentrations. A total of 43 operational taxonomic units (OTUs) were obtained from the four groups, which were categorized into 7 phyla, 9 classes, 18 orders, 21 families, and 26 genera. Winogradskyella was the dominant genus in the groups with 2.5 and 100 mg/L nitrogen, while Marinobacter and Winogradskyella were relatively abundant in the groups with 50 and 100 mg/L nitrogen. Functional analysis using PICRUST2 showed that the three most abundant gene functions were carbohydrate metabolism, amino acid transport and metabolism, ribosomal structure and biogenesis, and energy production and conversion. BugBase phenotypic analysis revealed that there were no significant differences in phenotypes between the groups with 2.5 and 10 mg/L nitrogen, while the group with 50 mg/L nitrogen exhibited higher abundance in aerobicity, biofilm formation, mobile genetic elements, and stress tolerance phenotypes. Most of the bacteria in this work belonged to the aerobic types. A redundancy analysis (RDA) of environmental factors demonstrated that nitrogen concentration showed a positive correlation with species changes in the groups with 10 and 50 mg/L nitrogen; chlorophyll a exhibited a positive correlation with species changes in the groups with 50 and 100 mg/L nitrogen. Nitrogen concentration significantly influenced the epibiotic bacterial community associated with O. borgei, leading to changes in dominant species and community structure. This study provides important references for understanding the functional characteristics of the epiphytic microbial community of O. borgei and the exploration of specific microorganisms.