Effects of heavy metals (Cd, pb, cu, zn, and ni) on ipomoea aquatica forsk. growth in soil containing metal-biochar application

Abstract

The combined heavy metal pollution in vegetable fields poses a threat to food security. In this study, three types of biochar – Wedelia trilobata (WB), Pennisetum sinese Roxb (PB), and coffee grounds (CB) – were applied to a heavy metal-contaminated soil at rates of 2% and 5% (w/w). A pot experiment was conducted to investigate the effects of these three different types of biochar on the growth two Ipomoea aquatica Forsk. cultivars in the soil, and related mechanisms. The results showed that the addition of the three types of biochar significantly increased soil pH and SOM content. WB and PB significantly increased the shoot biomass of I. aquatica Forsk. The 5% WB amendment significantly decreased the plant uptake of Cd, Pb, Zn, and Ni. But PB and CB amendments at 2% or 5% showed no consistent effects on plant uptake of Cd, Pb, Cu, Zn, and Ni. The multi-factor variance analysis showed that biochar type significantly influenced Cd, Pb, Cu, Zn, and Ni accumulation in plant shoot and root and Cd, Cu, and Zn concentration in rhizosphere. Interestingly, in some of the treatments with PB and CB amendments, total available heavy metals increased, indicating that heavy metals contained in the biochar might have been released into the soil. The results indicated that biochar feedstock should be ecologically friendly.