Intercropping with herbs minimizes cadmium availability through altering physicochemical dynamics and metabolite profiles in wheat rhizosphere

For the past few years, the production of safe crops in Cd-contaminated soil has attracted more and more attention, and the intercropping of wheat and herbaceous plants has gradually become an effective way. However, how the physicochemical and metabolic processes because of the intercropping change Cd availability are still unclear. In this study, we studied the influence of changes in soil physicochemical properties induced by intercropping of wheat with different herbs on soil Cd availability of Cd. Meanwhile, we innovatively studied the effect of intercropping on rhizosphere metabolites and evaluated the impact on Cd transfer. Results showed that the highest wheat biomass was presented in the intercropping system with the Cichorium intybus L. (W4) and Aus hypochondriacus L. (W5) increasing by 57.66% and 54.05% individually, compared with monocropping, while W1, W2, and W3 increasing slightly. Further, the Cd accumulation in wheat grains under W4 and W5 treatment decreased by 44.95% and 43.12%, respectively. Structural equation model confirmed that the increased pH, CEC contributed to the decreased Cd availability in soil, as well the changed metabolic profiles in wheat rhizosphere after intercropping. Specially, up-regulation of fatty acid metabolism allowed wheat plants to maintain a normal intracellular environment under stress conditions. Similarly, up-regulation of saccharide and amino acid metabolism induced the accumulation of sugars and proteins, which positively increased wheat biomass and Cd-binding proteins, thus inhibiting the migration of soil Cd into wheat tissue. Collectively, this study provided reasonable insights towards understanding the metabolic mechanisms how intercropping altered Cd availability.