Multiple facets of phytoplankton assemblages show seasonally divergent patterns between lentic and lotic waterbodies at high altitudes

Environmental and spatial factors play important roles in generating and maintaining biodiversity. However, little is known about the main environmental and spatial correlates of multiple facets (taxonomic, functional and phylogenetic) of freshwater communities at high altitudes, particularly in phytoplankton assemblages. We assessed the diversity patterns and structure of phytoplankton assemblages across the Qinghai Lake basin, a typical high-altitude region in the Qinghai-Tibet Plateau that encompasses the Qinghai Lake (ML) and its inflowing tributaries (IT). We found that assemblage structure and diversity facets differed between the ML and IT across summer and autumn. ML sites supported higher algal density (dominated by cyanobacteria) than IT sites, which were dominated by diatoms. This contrasts with the historical dominance of diatoms in this lake, and serves as an early warning of potential future algal blooms in this high-altitude biodiversity hotspots. Most taxonomic metrics were significantly higher in IT than in ML across seasons, whereas functional evenness, functional dispersion and taxonomic distinctness were higher in ML. This contrasting pattern likely results from lower competition pressures and more efficient resources use in lentic than running waters. Environmental and spatial variables influencing phytoplankton assemblages varied among diversity metrics, though environmental factors generally prevailed. However, spatial eigenvectors may also highlight the importance of mass effects on phytoplankton assemblages. This study enhance understanding of the patterns and main correlates of phytoplankton assemblages at high altitudes, and has implications for future management programs aimed at monitoring phytoplankton dynamics and assemblage trajectories in the Qinghai–Tibet Plateau and other extreme environments.