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

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.