Effect of biochar on rice starch properties and starch-related gene expression and enzyme activities

We determined the effects of biochar on starch properties and the activities of enzymes and expression levels of genes related to starch in two Japonica rice cultivars. The two rice varieties were subjected to five biochar treatments (0, control; and 5, 10, 20, and 40 t/hm²). In both rice varieties, the content of apparent amylose and resistant starch were lower in biochar treatments than in the control. The proportion of fa chains was higher and that of fb3 chain was lower in the biochar treatments than in the control. Starch viscosity and cooking taste quality were improved by the biochar treatments. In both rice varieties, the activity of granule-bound starch synthase was significantly decreased by biochar treatments, and the activities of soluble starch synthase, starch branching enzyme, and starch debranching enzyme were significantly increased. The transcript levels of genes encoding starch synthases and starch branching enzymes were significantly increased by biochar treatments. We conclude that biochar at a dose of 5-10 t/hm² can regulate the activity of starch-related enzymes, and this affects the type, content, and fine structure of starch. Therefore, the addition of biochar to soil can improve the viscosity and taste quality of rice starch.