Response of microbe-DOM interactions to bioavailability in heterogeneous water diversion systems

Dissolved organic matter (DOM) serves as the central organic carbon pool in water diversion systems, with its interplay with microorganisms critical to material cycling and water quality safety. While microbe-DOM interactions have been studied in individual aquatic environments, they remain poorly understood within the integrated context of long-distance water diversion systems. This study investigates the dynamic mechanisms underlying microbe-DOM interactions across multiple habitats (including rivers, reservoirs, and tunnels). We developed a dynamic, multi-stage conceptual model that links DOM heterogeneity to microbial metabolic strategies. Our research defines DOM molecule activity and collective metabolic potential across diverse aquatic habitats. Microorganisms control the ecological assembly process of the entire DOM pool through active DOM fractions (28 % of DOM pool) with high potential biotransformation (≥9). The Microbe-DOM Utilization Index (MDUI) was developed to quantify DOM utilization patterns. MDUI explained 64.12 % of DOM compositional variation. Based on MDUI values across DOM metabolic potentials, we derived the microbe-DOM utilization curve equation. This revealed a triphasic metabolic mechanism governed by alternating metabolic curves: the L-line, dominated by central metabolism of amino sugars and lipid-like proteins, and the H-line, driven by polymer degradation mediated by virus (Uroviricota) and bacteria (Actinobacteria). This proposed mechanism was subsequently validated through species niche, KEGG pathway, and enzyme activity analysis. This study provides a quantification of microbe-DOM interaction, represents the first discovery of microbial adaptive metabolic mechanisms in response to DOM bioavailability, thus providing a theoretical basis and methodological support for ecological security regulation of complex water diversion systems.