Foliar Spraying of Selenium Combined with Biochar Alleviates Cadmium Toxicity in Peanuts and Enriches Selenium in Peanut Grains

Abstract

Cadmium (Cd) pollution in soil, particularly in peanut production, is a problem that has attracted global concern and needs solutions urgently. Selenium (Se) can alleviate Cd toxicity; however, the underlying mechanisms are not completely understood. Therefore, two varieties of peanut (Arachis hypogaea Linn.), "Huayu 23" and "Huayu 20", were chosen as the target crops for this study. A pot experiment was conducted to investigate the effects of two Se application methods combined with biochar on the accumulation of Cd and Se, and the best application method was identified. In addition, the role of Se in alleviating Cd toxicity in peanuts was studied. The results indicated that both Se and biochar decreased the Cd content in peanuts and alleviated Cd toxicity. However, the combined application of foliar Se and biochar significantly increased the peanut biomass by 73.44-132.41%, increased the grain yield of Huayu 23 by 0.60-1.09 fold, and Huayu 20 by 2.38-3.48 fold. Additionally, Cd content in peanut grains was decreased by 32.81-50.07%, and Se content was increased by 31.57-99.75 folds. Biochar can decrease the absorption of Cd from the soil, while Se can increase the accumulation of Cd in cell vacuoles by increasing glutathione and phytochelatin to decrease the movement of Cd into the grains. Therefore, our results indicate that the combined application of foliar Se and biochar can effectively promote the enrichment of Se in peanuts and suppress Cd toxicity.

Keywords: cadmium; glutathione; phytochelatin; selenium; subcellular distribution.

Figure 1

Cadmium accumulation in the roots, stems, leaves, and grains of Huayu 23 and Huayu 20. (a) Huayu 23 with high cadmium pollution; (b) Huayu 20 with high cadmium pollution; (c) Huayu 23 with low cadmium pollution; (d) Huayu 20 with low cadmium pollution.

Figure 2

Subcellular distribution of cadmium in the leaves of Huayu 23 and Huayu 20. (a) Huayu 23 with high cadmium pollution; (b) Huayu 23 with low cadmium pollution; (c) Huayu 20 with high cadmium pollution; (d) Huayu 20 with low cadmium pollution. F1, F2, F3 and F4 are components of the cell wall, cell nucleus and chloroplast, mitochondria, and soluble cytoplasm, respectively.

Figure 3

Scanning electron microscope images and energy spectrum analysis of leaves of Huayu 23 under blank (a–c), single leaf selenium (d–f), and single soil selenium treatments (g–i). The red dots in the figure represent the selection points for energy spectrum analysis.