Effects of storage condition and duration on viability and starch metabolism in biochar-coated rice seeds

Seed storage conditions are critical determinants of rice seed viability and subsequent germination performance; however, the extent to which biochar-based seed coatings enhance storage tolerance and the underlying physiological mechanisms remain poorly understood. In this study, biochar-coated and uncoated rice seeds were stored for 0–8 months under three contrasting conditions: low temperature, room temperature with low humidity, and room temperature with high humidity. Seed germination characteristics, seedling establishment, respiratory metabolism, carbohydrate contents, activities of key starch-metabolizing enzymes, and changes in endosperm ultrastructure were systematically assessed. Low-temperature and room-temperature/low-humidity storage effectively maintained seed germination and seedling growth, whereas storage under room-temperature/high-humidity conditions for 4 (coated seeds) or 6 (uncoated seeds) months markedly accelerated seed deterioration. Across all storage regimes, biochar-coated seeds consistently exhibited higher germination percentages, improved emergence performance, and greater seedling biomass compared with uncoated seeds, with a pronounced delay in vigor decline under high-humidity conditions. Seed deterioration was closely associated with suppressed respiratory activity, reduced soluble protein levels, and impaired starch and sugar metabolism, as evidenced by declines in starch and soluble sugar contents, decreased activities of α-amylase, β-amylase, and sucrose synthase, and disruption of endosperm starch granule structure. In contrast, biochar coating partially maintained these metabolic processes and alleviated structural degradation of the endosperm. Overall, biochar coating enhances the storage tolerance of rice seeds under adverse storage conditions by preserving metabolic activity and endosperm structural integrity, highlighting its potential as an effective strategy to improve seed longevity and storage performance.