Silicon Supply through Subirrigation System Alleviates High Temperature Stress in Poinsettia by Enhancing Photosynthetic Rate

The effect of Si supplied during plant cultivation on tolerance to high temperature stress in Euphorbia pulcherrima Willd. 'Ichiban' was investigated. Rooted cuttings were transplanted into 10-cm pots and a complete nutrient solution, containing 0 or 50 mg·L -1 Si as either K2SiO3, Na2SiO3, or CaSiO3, was supplied through subirrigation or weekly foliar applications. After two months of cultivation, plants were placed in an environment-controlled chamber and subjected to 35 ± 1°C (high temperature) conditions for 18 days. Enhanced specific activities of enzymatic antioxidants (APX) and suppressed specific activities of non-enzymatic antioxidants (ELP) were observed in the high temperature-stressed plants with Si application. The Fv/Fm (maximum quantum yield of photosystem II), photosynthetic rate, and Si contents in the shoot increased in the treatments of K2SiO3 and Na 2SiO3 supplied through subirrigation. The Si-treated plants had more tolerance of high temperature stress than the control plants. Of the Si sources and application methods tested, K2SiO3 and Na 2SiO3 supplied through subirrigation were found to be the most effective in enhancing tolerance to high temperature stress.