Ecosystem-specific patterns in soil dissolved organic matter (DOM) biodegradability: Validated by a multi-property...

Soil dissolved organic matter (DOM) bio-stability is critical for understanding carbon (C) cycling and ecosystem functioning. Existing approaches for estimating DOM biodegradability are constrained by the need to balance accuracy, scalability, and cost-effectiveness, given DOM's chemical complexity and methodological limitations. Soil DOM is widely used as a proxy for soil organic matter (SOM) persistence, yet direct empirical validation remains scarce. Here, we applied an integrative index, the persistence index (PI), calculated using ecosystem multifunctionality frameworks based on multiple properties, including diverse optical properties, to evaluate DOM persistence. Soil DOM samples from forest, grassland, and cropland soils were subjected to 14-day biodegradation incubation experiments, and degradation kinetics were modeled using a double-exponential function to quantify labile and stable fractions. Biodegradability was ecosystem-specific, with forest soil DOM exhibiting the lowest degradability and the longest mean residence time (MRT), followed by grassland and cropland. PI values correlated strongly with biodegradation parameters: negatively with labile DOM and positively with stable fractions and MRT. Optical-derived PI mirrored these trends, confirming its promise as a rapid, cost-effective proxy for DOM stability. Furthermore, DOM biodegradability also showed significant correlations with SOM persistence metrics, highlighting the coupling between the solid and aqueous phases of SOM. These ecosystem-specific differences in DOM stability have direct implications for land-use management, integrated watershed stewardship, and climate mitigation strategies. This study highlights PI's robustness as a potential framework for cross-ecosystem comparisons, supporting methodological reference in environmental management, C sequestration, and contaminant risk reduction across diverse ecosystems.