Mediation of crop heavy metal uptake by root exudates in an intercropping system of heavy metal contaminated soils.

Background: Intercropping emerged as an agricultural technique exhibiting remarkable potential and benefits in promoting safe crop cultivation in heavy metal contaminated soils. In the present study, we set up five treatments of maize monoculture, soybean monoculture, Sedum Alfredii monoculture, maize/Sedum Alfredii and soybean/Sedum Alfredii intercropping and revealed the mechanism of intercropping on the yield of maize and soybean, as well as on the uptake of manganese (Mn), cadmium (Cd) and lead (Pb), from the perspective of root exudates by a randomized block test in the field.

Results: The results showed that intercropped maize yield increased by 16.35% compared to monoculture maize in the maize/Sedum alfredii system. Meanwhile, the contents of Mn, Cd and Pb in the rhizosphere soil of intercropped maize were lower than those of monoculture maize, with significant reductions in acid-soluble and reducible Mn and Cd. By contrast, the soybean/Sedum Alfredii intercropping system, showed no significant differences in soybean yield, heavy metal accumulation in organs, or rhizosphere soil concentrations between intercropped and monoculture soybeans. Further analysis of the maize rhizosphere microenvironment revealed that citric acid and malic acid, as secreted by intercropped maize roots, were key factors influencing the morphological transformation of Mn and Cd in the soil. These acids also reduced the absorption and accumulation of Mn and Cd in intercropped maize.

Conclusion: The findings of the present study provide critical insights into heavy metal uptake mechanisms in intercropping systems and offer a novel strategy for the sustainable remediation and utilization of heavy metal-contaminated farmland. © 2025 Society of Chemical Industry.