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 Qinghai Lake (QL) and its inflowing tributaries (IT). We found that assemblage structure and diversity differed between the QL and IT in summer and autumn. QL 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 hotspot. Most taxonomic metrics were significantly higher in IT than in QL both seasons, whereas functional evenness, functional dispersion, taxonomic diversity and average taxonomic distinctness were higher in QL. This contrasting pattern likely results from lower competition pressures and more efficient resource use in lentic than in lotic waters. Environmental and spatial variables influencing phytoplankton assemblages varied among different diversity metrics, although environmental factors generally prevailed. However, the significant effect of spatial eigenvectors may also highlight the importance of mass effect on phytoplankton assemblages. This study clarifies our understanding of the patterns and main correlates of phytoplankton assemblages in a high-altitude lake, and has implications for future management programs aimed at monitoring phytoplankton dynamics and assemblage trajectories in the Qinghai-Tibet Plateau and other extreme environments. • We studied spatio-temporal patterns and driving factors of multiple facets of phytoplankton assemblages in the Qinghai Lake basin. • Functional and phylogenetic diversity can add to information on species diversity in ecological monitoring and assessment. • Contrary to past surveys, the density of cyanobacteria in the main lake area was higher than that of diatoms. • Environmental factors played a stronger role than spatial constraints in shaping phytoplankton assemblages. • Salinity was the most influential predictor.