Effects of biochar on photosynthesis and antioxidative system of Malus hupehensis Rehd. seedlings under replant conditions

The purpose of this study was to investigate the mechanisms and effects of biochar on the plant growth of Malus hupehensis Rehd. seedlings under replant conditions. Before the M. hupehensis Rehd. seedlings were planted in pots, biochar was added to pots filled with replant soil at four rates: 0, 5, 20, 80 g kg−1. The growth of seedlings was monitored with plant height and photosynthesis. The antioxidant enzyme activities, lipid peroxidation and osmotic regulation substance contents in seedlings leaves were also measured. The phenolic compounds in the four soil treatments were detected too. The results showed that the addition of biochar significantly decreased the contents of phenolic acids in replant soil through the sorption of biochar. In comparison with the control, biochar applied to replant soil at 80 g kg−1 enhanced the plant height, fresh weight, and photosynthetic parameters. Furthermore, seedlings in soil treated with biochar, particularly at 80 g kg−1, exhibited higher activity of antioxidant enzymes including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. With the addition of biochar, the contents of malondialdehyde, O2•− and H2O2 significantly decreased, and the osmotic substances accumulation in leaves also declined. These results suggested that the addition of biochar can alleviate apple replant disease by activating antioxidant enzymes, decreasing lipid peroxidation, and significantly reducing the phenolic acids content of replant soil through the sorption of biochar.