Phytoextraction Potential of Legumes in Soil With High Bioavailable Manganese Content

Abstract

Manganese (Mn) toxicity is a significant threat to tropical ecosystems, yet specific regulatory limits and sustainable remediation strategies for acidic Oxisols remain scarce. A greenhouse experiment was conducted in a 4×4 factorial arrangement, utilizing an acidic Oxisol contaminated with Mn doses of 0, 50, 100, and 150 mg kg⁻¹, to evaluate the Mn storage capacity in Cajanus cajan, Canavalia ensiformis, Mucuna pruriens, and Crotalaria juncea, as well as the effect of the metal on gas exchange. The experiment was entirely conducted with manual irrigation of distilled water to avoid large variations in soil pH, thus ensuring high Mn availability was maintained throughout the experiment. Results showed that legume species had different abilities to phytoextract manganese as a function of soil availability, although they showed tendencies towards an increased root/shoot ratio under high Mn concentrations. Notably, M. pruriens demonstrated the highest tolerance to Mn doses up to 150 mg kg⁻¹, whereas sensitive species like C. cajan showed a 50% reduction in net photosynthesis. Ultimately, the physiological plasticity of M. pruriens allowed for superior compensatory capacity and the highest Mn accumulation among the tested species. By identifying critical soil Mn thresholds and species-specific physiological boundaries, these findings support the evolution of targeted phytoremediation.