Silicon Alleviates Temperature Stresses in Poinsettia by Regulating Stomata, Photosynthesis, and Oxidative Damages

The effects of silicon (Si) on temperature stresses were investigated in poinsettia. Well-rooted cuttings supplemented with and without Si were exposed to 40 degrees C, and plants treated with or without Si during cutting propagation and cultivation were subjected to 4 degrees C. The results showed that almost all the stomata of cuttings without Si supplementation were closed, while some of them were still open in cuttings supplemented with Si under a high temperature stress. However, Si was not able to alleviate stomatal closure of poinsettia under low temperature stress. The increased epicuticular wax might contribute to enhanced resistance of poinsettia to low temperature stresses. In addition, poinsettia maintained a higher photosynthetic rate and lower malonaldehyde and hydrogen sulfide concentrations when supplemented with Si under high and low temperature stresses, which might contribute to lower APX activities. Overall, temperature stresses had negative impacts on the physiological characteristics of poinsettia, while Si could alleviate some effects of temperature stresses.