Climate-Smart Remediation: Selenium-Biochar Dual Functionality Reduces Mercury Toxicity and Improves Selenium Biofortification in Garlic under Future CO2 Scenarios.

Elevated atmospheric CO2 combined with mercury (Hg) contamination threatens crop safety and human health. This study investigated the dual role of selenium-enriched biochar (SeBC) in mitigating Hg bioavailability and enhancing selenium (Se) nutrition in garlic (Allium sativum L.) under elevated CO2 (+200 ppm). The results revealed that while CO2 enrichment increased garlic biomass by 19.92-47.51%, it also raised Hg accumulation in bulbs (10.84%) and roots (23.18%). Conversely, SeBC application effectively reduced Hg concentrations in shoots, bulbs, and roots by 67.31%, 50.97%, and 52.97%, respectively, outperforming conventional biochar. Mechanistically, SeBC increased soil pH, promoted Hg-Se complexation, and enhanced Hg immobilization into residual forms. Additionally, SeBC increased plant Se content by 1.64% and reduced Hg translocation by 73.2%. These findings demonstrate SeBC's potential as a climate-smart strategy to simultaneously reduce Hg contamination and improve Se biofortification in crops, offering critical insights for sustainable agriculture and food safety management.