Straw-derived dissolved organic matter characteristics determine soil microorganism utilization strategies

Plant dissolved organic matter (PDOM) serves as a key intermediate during straw decomposition and influences the substrate utilization strategies of soil microbiota through its intrinsic chemical properties. In this study, gray desert soil collected from a 10-year continuous cotton straw return field was used for microcosm incubation. Two 13 C-labeled PDOM fractions were synthesized, including a hydrophilic component ( 13 C–IM, C/N = 9.61) and a hydrophobic component ( 13 C–OM, C/N = 69.88). By combining highly multiplexed amplicon profiling and DNA stable isotope probing (DNA-SIP), we systematically compared the substrate preferences, community succession, and coexistence patterns among taxonomic units in bacterial and fungal communities utilizing these two PDOM fractions. Bacterial species richness specialized in 13 C–IM and 13 C–OM utilization displayed opposite temporal dynamics, and shared bacterial species richness peaked on Day 1. Bacteria represented by Proteobacteria (0.35–0.58), Actinobacteriota (0.18–0.27), and Firmicutes prioritized utilization of hydrophilic 13 C–IM and formed more complex bacterial co‑occurrence networks at the early stage (Days 1–5; nodes: 372–564, edges: 24 188–41 756, average degree: 131–148, modularity: 0.54–0.64), while topological advantages shifted to 13 C–OM ‑associated bacteria on Day 45. By contrast, fungi dominated by Ascomycota (0.73–0.86) and Basidiomycota (0.13–0.25) underwent obvious community succession and were more adapted to hydrophobic 13 C–OM, constructing more complex early‑stage fungal networks (nodes: 80–135, edges: 1125–3346, average degree: 28–49), whereas late‑stage 13 C–IM fungal networks exhibited higher modularity. Fungal networks were persistently dominated by positive correlations across all incubation periods. PDOM chemical composition, incubation duration, and their interaction jointly modulated microbial community assembly and alpha diversity. These findings show that hydrophilic and hydrophobic PDOM fractions drive divergent substrate utilization strategies by restructuring the composition and co-occurrence networks of microbial communities, thereby yielding new insights into the mechanisms of soil carbon cycle and the optimization of straw-return management.