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Objective To compare the compositional differences, assembly characteristics, and ecological roles of generalist and specialist microeukaryotes between the dry and rainy seasons in the lower reaches of the Yarlung Zangbo River and to clarify how spatial heterogeneity and seasonal hydrological fluctuations influence microeukaryotic diversity. Methods Water samples were collected from 34 paired sampling sites in May 2022 (dry season) and July 2023 (rainy season). Environmental factor measurements, 18S rRNA gene high-throughput sequencing, and multivariate statistical analyses were conducted to examine the assembly processes, environmental responses, species associations, and state-transition characteristics of the generalist and specialist subcommunities. Results A total of 14 828 high-quality amplicon sequence variants (ASVs) were obtained, with 10 240 and 8 737 detected in the dry and rainy seasons, respectively. In the dry season, 146 generalists and 933 specialists were identified, whereas 526 generalists and 1 420 specialists were identified in the rainy season. The relative abundance of generalists and specialists was 6.29% and 73.18% in the dry season and 4.45% and 77.49% in the rainy season, respectively. The composition of generalists and specialists differed significantly in both seasons, and beta diversity was mainly driven by species turnover. Stochastic processes generally dominated community assembly, although the relative contributions of ecological processes differed between the two ecological strategy groups. In the rainy season, dispersal limitation weakened in specialists, whereas the contribution of deterministic processes increased in generalists, mainly due to increased homogeneous selection. Binary-state speciation and extinction (BiSSE) parameters indicated that specialists had higher state-transition rates, suggesting faster state turnover under contrasting seasonal conditions. Spatial and water physicochemical factors jointly drove community differentiation and niche divergence, with latitude, turbidity, and chemical oxygen demand as the main explanatory variables. Co-occurrence network analysis showed that both groups contributed to maintaining network complexity and stability, while network simplification was more pronounced after specialists were removed. Conclusion Generalist and specialist microeukaryotes in the lower reaches of the Yarlung Zangbo River showed marked differences in community assembly across seasonal transitions. Their distribution was jointly shaped by spatial heterogeneity, hydrological connectivity, and environmental filtering. Specialists contributed more strongly to network connectivity and may play a more important role in maintaining community resilience than generalists.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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