Abstract
<title>Abstract</title> <p>Global change and anthropogenic activities have accelerated lake salinization in arid and semi-arid regions of northern China, while plankton communities and ecosystem functions are highly sensitive to salinity variation. However, how plankton diversity patterns, community assembly, and functional regulation respond to continuous salinity gradients remains poorly understood. Here, four lakes on the Inner Mongolia Plateau were selected to represent a natural gradient from freshwater to brackish and low-salt conditions. Based on field surveys, taxonomic identification, and integrated analyses including ANOVA, NMDS, SEM, and DNCI, we investigated the effects of salinity on plankton community structure, multidimensional diversity, assembly processes, and ecosystem functioning. Salinity strongly shaped plankton community composition and caused a significant linear decline in taxonomic alpha diversity and functional richness. In contrast, beta diversity showed nonlinear patterns associated with changes in turnover and nestedness contributions. SEM indicated that species richness promoted functional traits, whereas biodiversity and ecosystem functioning were partially decoupled under salinity stress. Community assembly was dominated by deterministic processes across the gradient (DNCI < − 2), with stronger environmental filtering in freshwater and low-salt lakes and greater stochasticity in brackish waters.Phytoplankton exhibited stronger declines in taxonomic α-diversity under salinity stress, while zooplankton assembly processes were more sensitive to intermediate brackish conditions.These findings enhance understanding of salinity-driven ecological processes and provide insights for conserving salinizing inland lake ecosystems.</p>