Elevational and anthropogenic gradients drive divergent assembly mechanisms of free-living and particle-attached bacterioplankton in Chinese lakes

Understanding the assembly mechanisms of bacterial communities is pivotal for deciphering biogeochemical cycles and ecosystem functioning in lacustrine systems. However, systematic comparisons of community assembly processes between free-living (FL) and particle-attached (PA) bacterioplankton across distinct geographic regions remain limited. Here, we employed high-throughput 16S rDNA sequencing, null models, and Raup-Crick analyses to investigate bacterial communities in plateau (Yunnan) and plain (Yangtze River Delta) lakes in China, characterized by contrasting anthropogenic pressures. Results revealed that stochastic processes, particularly homogenizing dispersal, dominated FL bacterial assembly in both regions. In contrast, PA communities exhibited spatial divergence: stochastic processes prevailed in plateau lakes, while deterministic processes governed anthropogenically impacted plain lakes. Mantel tests identified mineral ions (e.g., Co, V, Pb) as critical regulators of PA community assembly, alongside traditional factors like nutrients, phytoplankton (chlorophyll a ), and submerged macrophytes. Notably, stochasticity increased with trophic status, driven by enhanced drift in eutrophic waters. Our findings underscore the interplay between bacterial lifestyle, environmental heterogeneity, and anthropogenic impacts in shaping microbial assembly, providing critical insights for predicting ecological responses to environmental change. • Homogenizing dispersal is a dominant process shaping free-living (FL) bacterial communities across regions. • Deterministic processes govern particle-attached (PA) assemblages in human-impacted plain lakes. • Co, V, and Pb have a critical influence on PA assemblages, surpassing traditional nutrient drivers. • Stochasticity rises with trophic status via ecological drift. • PA divergence highlights anthropogenic overrides of natural barriers.