Elevated CO2 enhances Pb availability and desorption kinetics at the root-soil interface: Role of dissolved organic matter in soil solution.

Understanding the ecological forces driving lead (Pb) translocation, distribution, and accumulation in plant‒soil ecosystems under elevated CO2 (eCO2) is essential for optimizing phytoremediation strategies and predicting Pb cycling dynamics. This study systematically investigated Pb availability and desorption kinetics in a root-soil ecosystem with the metal-tolerant plant Trifolium repens L., using diffusive gradients in thin films (DGTs), fluorescence spectroscopy, and kinetic modelling. Our results show that eCO2 increased free Pb2+(aq) concentrations by 217.6-416.0 %, while concurrently reducing stable Pb‒humic complexes by 3.2-22.3 %. Moreover, eCO2 significantly increased DGT-labile Pb concentrations and accelerated diffusion-limited resupply rates, indicating increased Pb resupply to the soil solution despite the rapid depletion of the rhizosphere labile Pb pool. Fluorescence spectroscopy with parallel factor analysis revealed substantial alterations in dissolved organic matter (DOM) compositions under eCO2, characterized by elevated amino acid-like substances and microbial metabolites. Fluorescence indices confirmed the enhanced DOM biological activity and reduced humification. Procrustes and redundancy analyses identified dissolved organic carbon content and humic-like DOM fractions as critical determinants of Pb speciation and bioavailability. Our findings elucidate a mechanistic framework that links CO2-induced rhizosphere DOM processes to enhanced Pb-specific phytoremediation outcomes, addressing existing uncertainties in climate‒Pb interactions. We demonstrate that eCO2 selectively activates specific chemodynamic pathways enhancing predictions of terrestrial Pb cycling under climate change and provide actionable strategies to optimize nature-based remediation practices in future climate scenarios. Further research should extend these findings across a broader range of ecological types and explicitly consider multiple global change factors such as temperature and precipitation variations.