Microbial and Molecular Responses of DOM to Nutrient Enrichment in Paddy Soils
Despite the critical role of dissolved organic matter (DOM) dynamics in soil carbon sequestration, the molecular mechanisms by which nutrient enrichment modulates DOM transformation remain poorly understood. Here, we used high-resolution mass spectrometry and high-throughput sequencing to investigate nutrient gradient effects on DOM transformation and microbial mechanisms in green manure-amended paddy soils. We show that nutrient enrichment increases DOM stability, shifting composition toward recalcitrant condensed aromatics/tannins while reducing lignin and molecular diversity. These changes coincide with a decline in the transformation potential of DOM, as microbial processes responsible for DOM processing were inhibited. Notably, soil pH, emerged as a key mediator, linking nutrient-induced acidification with decreased microbial activity and impaired DOM bioavailability. These findings establish a nutrient-pH-microbe regulatory framework, guiding nutrient management strategies to balance carbon sequestration and ecosystem resilience in agricultural soils.