Biochar application on heavy metal immobilization in unsaturated soil with vegetation: a review

ABSTRACT Biochar, a type of soil amendment, is widely used in heavy metal–polluted soil. It is also effective in enhancing plant performance. However, how biochar affects the soil heavy metal toxicity considering the plant–soil interactions is not well summarized. Therefore, this paper aims to review and summarize the effects of biochar on heavy metal availability in vegetated unsaturated soil. First, this review summarizes the effects of biochar on key parameters of unsaturated soil, including pore size distribution, water permeability, water retention curve, nutrient cycling and soil biota. Then, the mechanism of biochar for managing heavy metals in soil with vegetation is discussed, with a focus on both physical and biochemical aspects. Additionally, the impact of biochar-induced plant growth on the availability of heavy metals in the plant–soil system is explored. Finally, suggestions for future research and applications of biochar are provided. This paper supplies novel outlooks for further study and practice.