Wood Vinegar Enhances Seedling Rate of Rice Seeds under Flooding Stress by Mitigating Oxidative Damage and Maintaining Energy Homeostasis

Flooding stress is the main adverse condition during the emergence period of direct-seeded rice. This study investigated the use of wood vinegar as a seed soaking treatment to enhance rice emergence rates under flooding stress, exploring both the methodology and physiological mechanisms involved. The optimal seed soaking concentration was determined through a gradient experiment, followed by a multi-cultivar validation test, and the physiological mechanism of wood vinegar soaking on seedling emergence was analyzed by measuring the electrical conductivity (EC) of the flooding water, the starch and soluble sugar content changing in the grain and sprouts, and the dynamics of α-amylase activity and antioxidant-related enzyme activities in sprouts. The results showed that soaking rice seeds in wood vinegar solution at a low concentration significantly enhanced the emergence of rice seedlings under flooding conditions, with the 100-fold dilution having the most pronounced effect, increasing the seedling emergence rates by 50.6%–60.0%. Further analysis found wood vinegar treatment enhanced seedling establishment by inducing a significant increase of α-amylase activity, leading to a 74.9%–213.6% increase in soluble sugar content in sprouts during 2–8 d after flooding stress compared with the CK. Additionally, the treatment increased superoxide dismutase (SOD) and peroxidase (POD) activities in the sprouts, mitigating the lipid peroxidation of the cell membranes, and notably lower water electrical conductivity (EC) was observed in wood vinegar-treated seeds compared with CK. In conclusion, soaking rice seeds in 100-fold diluted wood vinegar solution improves rice seedling emergence rate under flooding stress by mitigating oxidative damage and maintaining energy supply. This approach is valuable for developing cost-effective seed treatment technology, offering novel strategies to improve seedling emergence rate and uniformity of direct-seeded rice under flooding conditions.