Oxygen Release Compound Alleviates Injuries of Chrysanthemum under Waterlogging and High Temperature Conditions

Heavy summer rain in subtropical and tropical areas causes soil hypoxia, which is detrimental to field-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitam.]. Oxygen release compound (ORC), mainly composed of magnesium peroxide, may alleviate injuries of chrysanthemum under waterlogging as ORC can release oxygen when solved in water. The effect of ORC on growth and photosynthesis were studied in two chrysanthemum cultivars, waterlogging-tolerant ‘Huang Gin-Ging’ and waterlogging-intolerant ‘Kaa Dei-Na’. Vegetative young plants with 14-16 leaves were placed in a growth room at 30/25℃ and 12 h photoperiod with an average light intensity 220 μmol·m^-2·s^-1. Plants were subjected to three treatments: normal irrigation (control), waterlogging treatment (3-day waterlogging followed by 9-day recovery), and ORC treatment (80 mL of 1.0 g·L^-1 ORC solution applied to the medium one day before the waterlogging treatment). Results showed that control plants of both cultivars grew well and maintained high photosynthesis rates. As compared with control, waterlogging treatment caused more root dry weight reduction in ‘Kaa Dei-Na’ than ‘Huang Gin-Ging’ (52.3% vs. 7.8%). Plants of ‘Huang Gin-Ging’ at waterlogging or ORC treatments did not differ in growth and exhibited a declined net photosynthesis (Pn) at Day 3 but a recovered Pn at Day 12. In contrast, ‘Kaa Dei-Na’ at ORC treatment had greater shoot length and root dry weight, consistently higher Pn and lower intercellular space CO₂ concentration than those at waterlogging treatment. ORC application prior to waterlogging resulted in increased growth and Pn and alleviated the injury of waterlogging-intolerant ‘Kaa Dei-Na’.