• Chemical modifications reduced Cu²⁺ binding in citrus root cell walls. • Carboxyl groups were the dominant sites for Cu²⁺ adsorption. • Cu²⁺ adsorption followed pseudo-second-order kinetics. • Langmuir model indicated monolayer chemisorption of Cu²⁺. Copper (Cu) accumulation in orchard topsoil resulting from intensive agricultural inputs has become a global challenge, threatening citrus productivity and soil sustainability. The eco-friendly strategies for Cu immobilization are urgently needed. Plant cell wall modification induced by abiotic stress regulates functional group composition and Cu 2+ binding capacity at the subcellular level. However, its role in Cu²⁺ adsorption and the dominant binding groups in citrus roots remain unclear. In the present study, the root cell wall of Citrus sinensis was isolated and chemically modified through amino methylation, pectin removal, and esterification to investigate the mechanisms governing Cu²⁺ adsorption. The Fourier Transform Infrared Spectroscopy (FTIR) analyses, the adsorption kinetics and the isothermal analyses demonstrated that cell wall modification significantly altered chemical group characteristics and adsorption behavior. Compared with the control, Cu²⁺ adsorption capacity decreased by 19.11 %, 26.88 % and 77.24 % in aminomethylated, pectin-removed, and esterified cell walls, respectively, confirming the dominant contribution of carboxyl groups to Cu²⁺ binding in C. sinensis roots. The adsorption data were well described by the pseudo-second-order kinetic model and the Langmuir isotherm, indicating a monolayer chemisorption process. These results reveal how cell wall remodeling regulates Cu²⁺-binding in citrus roots, advancing understanding of plant adaptation to Cu toxicity. The study also demonstrates the potential of modified citrus biomass as a sustainable Cu²⁺ adsorbent, providing a plant-based solution with relevance for heavy-metal remediation in agricultural systems.
Lu et al. (Sun,) studied this question.