Rainfall re-engineered by plant functional types in the urbanized Chaohu Lake Basin: Differential regulation of DOM molecular size, nutrient, and metal dynamics

Urban vegetation canopies significantly alter the biogeochemistry of atmospheric deposition, yet the molecular-level characteristics of leached dissolved organic matter (DOM) and nutrient dynamics remain poorly understood. We investigated the hydrochemical transformation of precipitation by two distinct plant functional types. Across 17 storm events, paired rainfall and throughfall samples from eight urban plant species (five shrubs, three arbors) were characterized using high-performance size-exclusion chromatography (HP-SEC), three-dimensional excitation–emission matrix fluorescence spectroscopy (3D-EEMs), and nutrient flux quantification. Results revealed markedly divergent nutrient leaching behaviors. Arbor throughfall exhibited a net increase in total nitrogen (TN) flux of 433.99 kg/km 2 relative to incident rainfall and a higher nitrogen/phosphorus ratio of 13.73, whereas shrub throughfall showed a 3.5-fold greater net increase in phosphorus flux than arbor throughfall and substantial dissolved organic carbon (DOC) export. Crucially, HP-SEC demonstrated a fundamental restructuring of DOM. Shrub leachates exhibited high aromaticity and their concentration of high-molecular-weight aliphatic biopolymers was nearly double that of arbors, significantly altering the bioavailability and environmental reactivity of canopy-derived carbon. Multivariate analysis revealed strong associations between canopy-derived DOM and inorganic constituents, suggesting that DOM may contribute to their co-transport through potential complexation and carrier effects. Overall, these results provide site-specific evidence that vegetation type can influence the chemical composition and throughfall-mediated transport of DOM and nutrients, with potential implications for nutrient delivery to receiving waters and the management of urban vegetation.