Effects of biochar amendment on relieving cadmium stress and reducing cadmium accumulation in pepper

Biochar is widely used in agricultural soils or heavy metal-polluted soils to improve the quality of the soils, which would affect the growth of the plant. However, the information of biochars' effect on the plant growth was still lacking, especially for the physiological response of the plant. Pot experiments were used to examine the effect of willow-derived biochars at two temperatures (450 and 600 °C) on cadmium (Cd) accumulation in pepper and to reveal the response of physiological parameters to exogenous Cd stress (1 and 5 mg/kg). The results showed that the accumulation of Cd in pepper roots was higher than that in pepper shoots. For low level of Cd treatments, high additional rates of the biochars could obviously reduce the accumulation of Cd in the pepper roots. Moreover, there was a negative correlation between the C content of the biochar-amended soils and the Cd content of the pepper root, suggesting that the application of biochar to the soil decreased the Cd accumulation in the root. A positive relationship between the H/C ratios of biochar-amended soils and their corresponding Cd concentrations in pepper root indicated that low thermal temperature-derived biochar could play an important role in immobilizing Cd in the soil. Furthermore, on the condition of low Cd level of treatments, the malondialdehyde content decreased in biochar-amended soils, especially at high biochar application rate. The chlorophyll content increased with increasing the rates of the biochar application. The physiological parameters indirectly proved that the application of biochar did not always alleviate the toxic effects of Cd on pepper leaves at high Cd concentration.