Silicon-mediated metal uptake dynamics in Sesuvium portulacastrum: Unveiling mechanisms for enhanced phytoremediation in coastal wetlands

Abstract

Coastal wetlands face dual pressures from high salinity and heavy metal pollution, presenting significant ecological challenges. Halophytes like Sesuvium portulacastrum possess unique physiological mechanisms to mitigate metal toxicity. This study investigates how silicon (Si) availability influences the accumulation of copper (Cu) and cadmium (Cd) in S. portulacastrum. Our results show that Si supplementation at environmentally relevant levels significantly increases Cu and Cd concentrations in the roots, while simultaneously reducing the root-to-shoot translocation of these metals. In situ non-invasive micro-testing revealed decreased metal efflux from the xylem, indicating an enhanced retention of metals in the roots. Furthermore, analyses using X-ray photoelectron spectroscopy and atomic force microscopy demonstrated a higher density of oxygen-containing functional groups and SiO⁻ on the extracellular matrix of Si-enriched roots. This structural transformation resulted in a significant reduction in root surface potential, facilitating greater metal ion attraction and uptake. The findings from this study provide critical insights into the mechanisms by which Si availability regulates metal accumulation in halophytes, suggesting potential strategies for mitigating metal pollution in coastal wetland ecosystems.