Active aluminum promoted copper uptake by Chinese cabbage grown in an acidic Cu-contaminated soil: A new insight with the diffusive gradients in thin-films technique (DGT)

Aim

To examine the effect of active aluminum (Al) on copper(II) (Cu(II)) bioavailability in an acidic Cu-contaminated soil and uptake of Cu(II) by Chinese cabbage.

Methods

A pot trial was conducted with Ca(OH)₂ and peanut straw biochar (PB) to investigate Cu(II) uptake by Chinese cabbage. DGT (C_DGT-Cu) and CaCl₂ extraction methods (C_CaCl2-Cu) were used to determine soil available Cu(II) and BCR sequential-extraction was used to determine Cu(II) species in the soil.

Results

The amelioration of soil acidity with Ca(OH)₂ and PB increased soil pH, promoted Chinese cabbage growth, and decreased Cu(II) uptake by plant shoots/roots. There were highly significant positive linear correlations between C_DGT-Cu, C_CaCl2-Cu and Cu(II) uptake by plant shoots. C_DGT-Cu showed a better predictive effect for Cu(II) uptake by plant roots with a greater correlation coefficient (R² = 0.9756). Thus, the DGT method was more effective in predicting Cu(II) uptake by plants. With increasing soil pH, Cu-HOAc and Cu-Reducible were converted to Cu-Residual, resulting in a decrease in soil Cu(II) bioavailability. The results of Structural Equation Modeling analyses showed that Al uptake by Chinese cabbage had a promoting effect on Cu(II) uptake by the plant, mainly through affecting plant growth indirectly. Soil exchangeable Al inhibited root growth (root length, root dry weight), reduced root resistance of Chinese cabbage and indirectly increased Cu(II) uptake.

Conclusions

Reducing Al toxicity decreased root damage and Cu(II) uptake by plant, improving the edible quality of Chinese cabbage. When remediating acidic Cu-contaminated soils, more attentions should be payed to mitigating and regulating Al toxicity.