Plankton diversity, heterogeneous cross-trophic associations and community assembly across four hydrochemically contrasting plateau lakes in northern China

Lake salinization is intensifying across arid and semi-arid regions, yet its ecological signal often covaries with lake-specific hydrochemistry and hydrology. We surveyed phytoplankton, zooplankton and water chemistry at 51 sites in four lakes in the Inner Mongolia Autonomous Region, China. The lakes differed markedly in total salts, electrical conductivity, nutrients and organic-matter indicators. Plankton composition, density and taxon diversity also varied among lakes, and Wuliangsu Lake supported the highest mean site-level richness. Models accounting for lake identity revealed limited evidence for consistent within-lake relationships between total salts and phytoplankton or zooplankton richness and Shannon diversity. Cross-trophic density associations showed evidence of among-lake heterogeneity, although this evidence weakened after exclusion of the high-leverage J7 site; no comparable heterogeneity was detected for taxon-richness associations. Pairwise DNCI intervals fell below zero in all phytoplankton comparisons and three zooplankton comparisons, while the three zooplankton comparisons involving JYH overlapped zero. These findings show that plankton variation across the four lakes was associated with contrasting hydrochemical and hydrological settings and heterogeneous cross-trophic numerical associations rather than a single salinity response.