[Environmental Screening Drives the Assembly Process of Periphytic Algae Community in the Lower Reaches of Yarlung Zangbo River].

Periphytic algae is an important primary producer in the river ecosystem, and it is one of the important indicators for the monitoring and evaluation of river water ecology. As a typical plateau river, the assembly process of the algae community in the Yarlung Zangbo River is still unclear. In May 2022 and July and September 2023, algae samples were collected, and water environmental factors were determined in the lower reaches of the Yarlung Zangbo River. The algal species were identified, and cell abundance and biomass were calculated using in vivo observation and fixed staining techniques to explore the diversity pattern of algae communities in the lower reaches of the Yarlung Zangbo River, to clarify the relative importance of deterministic and random processes in the assembly of algal communities, and to reveal the influencing factors driving the assembly process. The results showed that there were significant differences in the time of water environmental factors, mainly concentrated between spring, summer, summer, and autumn. A total of 274 species of algae were identified in the three seasons, belonging to 7 phyla, 9 classes, 18 orders, 31 families, and 63 genera, and the community differences between seasons were significant （P=0.001）. They all showed Bacillariophyta-Chlorophyta-Cyanophyta, and the community assembly process of algae was affected by both a deterministic process and random process but was dominated by the deterministic process. The interspecific relationship was mainly cooperative, and the co-occurrence network in autumn showed stronger network complexity and connectivity. The pH and turbidity were important water environmental factors affecting the community structure of algae, which could indirectly affect the community assembly process of algae by driving the metabolic rate and ecological adaptability of algae species.