Trait-niche relationships accompany the increasing topological prominence of abundant bacteria along a glacial-lake chronosequence.

Accelerated glacial retreat driven by global warming has rapidly expanded glacial lakes on the Qinghai-Tibet Plateau (QTP), creating natural laboratories for recording the successional trajectories of alpine aquatic ecosystems. However, how trophic succession during lake development drives microbial functional reorganization and reshapes core network positions remains unclear. Focusing on 15 glacial lakes on the QTP, this study integrated 16S rRNA gene sequencing, functional gene prediction, and topological network analysis to compare the adaptive trajectories of abundant and rare bacterial taxa along the successional gradient. Results indicated that both subcommunities exhibited significant linear niche contraction with lake development, demonstrating progressive niche specialization. At the community-trait level, abundant taxa showed a pronounced decline in abundance-weighted mean rRNA operon copy number (RCN) along the gradient, consistent with reduced potential growth responsiveness. This shift was accompanied by an increased predicted recalcitrant-to-labile carbon degradation gene ratio and a decreased predicted nitrogen fixation-to-nitrification gene ratio. Topological analysis further revealed that abundant taxa were disproportionately represented among highly central and topologically identified putative keystone positions, and this representation increased along the gradient. PLS-SEM further revealed contrasting patterns of association among environmental variation, community-level trait proxies, niche specialization, and network topology between abundant and rare taxa. Together, these findings suggest that abundant taxa become increasingly important in the topological organization of bacterial communities during glacial-lake development, providing new insight into microbial community reorganization under ongoing glacier retreat.