{ "abstract": "The upper Chishui River in Zhaotong, Yunnan, is a typical karst headwater stream and remains the only undammed first-order tributary of the upper Yangtze River. Agricultural and urban land use creates a distinct longitudinal nutrient gradient. We investigated the responses of planktonic bacteria and fungi to seasonal hydrology and anthropogenic disturbances, as well as their community assembly processes. Surface water samples were collected in the dry season (January 2025) and wet season (May 2025) from three sites: an upstream least-disturbed reference site (CSY), a midstream site affected by agricultural and township runoff (GZ), and a downstream site receiving municipal wastewater discharges (EL). Using high-throughput amplicon sequencing of bacterial 16S rRNA genes and fungal ITS2 regions, we found that total nitrogen and total phosphorus increased downstream; seasonal hydrological variation altered nutrient concentrations but did not shift the overall spatial pattern. Nutrient and carbonate-related variables (pH and TP) were correlated with the community structure of both bacteria and fungi. Alpha diversity was highest at the upstream site. At midstream and downstream sites, species richness increased while community evenness declined in the dry season. Microbial community composition exhibited clear seasonal turnover: Flavobacterium dominated upstream in the wet season, while Limnohabitans prevailed at the midstream site in the dry season. Upstream fungal communities were enriched in terrestrial saprotrophs and plant pathogens, whereas Rozellomycota predominated downstream. Functional predictions based on Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2) and FUNGuild (Fungi + Functional + Guild) indicated that stress-response pathways were relatively abundant in the wet season. In contrast, carbohydrate and amino acid metabolism pathways were relatively more abundant in the dry season. Fungal trophic guild diversity at midstream and downstream sites also increased in the dry season. Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis (iCAMP) indicated that homogeneous selection predominantly structured bacterial communities across both seasons. By comparison, fungal communities shifted from homogeneous selection in the wet season to dominance by stochastic processes (e.g., ecological drift) in the dry season. Collectively, these findings suggest that bacteria and fungi respond differently to anthropogenic stress and seasonal hydrology in karst headwaters, with substantial seasonal divergence in their core community assembly mechanisms. Rozellomycota and certain fungal trophic guilds may serve as candidate bioindicators of chronic disturbance, pending further validation. These results provide a foundation for ecological health assessment and water resource conservation in karst headwater streams.", "abstract_shown": true, "affiliations": [ "College of Agronomy and Life Sciences, Zhaotong University", "Yunnan Engineering Research Center of Green Planting and Processing of Gastrodia, Zhaotong University", "Advanced Institute of Ecological Agriculture and Biodiversity on the Yunnan-Guizhou Plateau, Zhaotong University", "Yunnan Key Laboratory of Smart Villages and Agri-Cultural-Tourism Integration, Zhaotong University", "College of Agronomy and Biotechnology, Yunnan Agricultural University" ], "article_type": "research article", "arxiv": null, "author_total": 9, "authors": [ { "affs": [ 0, 1, 2, 3 ], "name": "Defu Liu" }, { "affs": [ 0 ], "name": "Wei Zheng" }, { "affs": [ 4 ], "name": "Hao Wen" }, { "affs": [ 0 ], "name": "Chaohuan Yang" }, { "affs": [ 0 ], "name": "Die Qu" }, { "affs": [ 0 ], "name": "Kaimei Zhang" }, { "affs": [ 0 ], "name": "Yongjie Xie" }, { "affs": [ 0 ], "name": "Guiliang Ji" }, { "affs": [ 0, 1, 2, 3 ], "name": "Zhenyue Feng" } ], "bibtex": "https://research.draconitic.com/paper/08qp3x914m6rt.bib", "cited_by": 0, "doi": "10.3389/fmicb.2026.1949002", "fulltext_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13727556/?tool=EBI", "id": "08qp3x914m6rt", "issns": [ "1664-302X" ], "landing_url": "https://www.frontiersin.org/articles/10.3389/fmicb.2026.1949002/full", "language": "eng", "licence": "CC-BY-4.0", "licence_label": "CC BY 4.0", "licence_source": "article", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "heading", "Original Research" ], [ "openalex", "2303|Microbial Community Ecology and Physiology" ] ], "openalex": "W7223044003", "pdf_url": "https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2026.1949002/pdf", "pmcid": "PMC13727556", "pmid": "42978729", "published": "2026-10-20", "publisher": "Frontiers Media SA", "ris": "https://research.draconitic.com/paper/08qp3x914m6rt.ris", "sources": [ { "first_seen": "2026-10-30T12:19:12Z", "native_id": "10.3389/fmicb.2026.1949002", "source": "crossref", "url": "https://www.frontiersin.org/articles/10.3389/fmicb.2026.1949002/full" }, { "first_seen": "2026-11-04T15:20:45Z", "native_id": "PMC:PMC13727556", "source": "europepmc", "url": "https://europepmc.org/article/PMC/PMC13727556" }, { "first_seen": "2026-11-06T12:23:24Z", "native_id": "PMC13727556", "source": "pmc", "url": "https://doi.org/10.3389/fmicb.2026.1949002" } ], "subjects": [ { "field": "biology", "origin": "openalex:2303|Microbial Community Ecology and Physiology", "subfield": "ecology" } ], "title": "Responses and assembly mechanisms of planktonic bacterial and fungal communities in the upper Chishui River during dry and wet seasons", "title_text": "Responses and assembly mechanisms of planktonic bacterial and fungal communities in the upper Chishui River during dry and wet seasons", "type": "peer-reviewed", "updated_at": "2026-11-07T12:20:43Z", "url": "https://research.draconitic.com/paper/08qp3x914m6rt", "venue": "Frontiers in Microbiology", "versions": [] }