Rewiring biogeochemical interactions: How interbasin water transfers shape DOM-Microbe dynamics

Interbasin water transfers (IBTs), large-scale engineered projects that redistribute water across basins, are reshaping inland hydrology and potentially altering biogeochemical processes. Yet, the mechanisms by which two critical components of biogeochemical cycling, dissolved organic matter (DOM) and microbial communities, are modulated under large-scale hydrological modification from IBTs remains largely unexplored. In this study, we combined advanced chemical (Fourier transform ion cyclotron resonance mass spectrometry) and genetical (high-throughput sequencing) tools to elucidate how DOM-microbe coupling is rewired by hydrological alteration of the Middle Route of China's South-to-North Water Diversion Project. Combining these techniques with network analysis revealed that IBTs alter DOM and microbial community composition. IBT-receiving waters exhibited higher abundances of labile DOM (+70%), Cyanobacteriota and Actinomycetota, and enhanced DOM-microbe interactions relative to non-receiving waters. Rare taxa played a key role in DOM-microbe coupling, with markedly stronger coupling observed in receiving waters. DOM molecular traits emerged as the primary driver, shaping microbial communities and, in turn, modulating DOM-microbe coupling pathways in hydrologically altered ecosystems. These findings provide new mechanistic insights into DOM-microbe responses to human-made water diversions, advancing our understanding of how biogeochemical processes changed due to large-scale hydrological engineering.