Effects Of Different Concentrations Of Exogenous CaCl₂ On Cold Resistance Of Zelkova Schneideriana

Zelkova schneideriana was a unique and rare tree species in China and has important economic value.Zelkova Schneideriana was mainly distributed in southern cities of China.It was difficult to survive in winter after being introduced to Shanxi.In this study,the five-year-old seedling of Zelkova schneideriana were treated with different concentrations of CaCl₂ by the method of foliage spraying,by analyzing the physiological indexes of leaves and branches and the changes of cold-resistant parameters,such as the sprouting rate of branches in the following year,the changes of indexes of Zelkova schneideriana seedlings in the process of cooling down in autumn and winter were compared.The effect of exogenous CaCl₂ on the cold resistance of Zelkova schneideriana at natural low temperature was studied,the mechanism of improving the cold resistance of Zelkova schneideriana by CaCl₂ was revealed,and the effect of CaCl₂ on the cold resistance of Zelkova schneideriana was comprehensively evaluated,the results would provide theoretical and practical basis for improving the winter hardiness of Zelkova schneideriana.The findings were as follows:1.The bound water/free water of Zelkova schneideriana was increased by different concentration of exogenous CaCl₂ with the decrease of temperature,the bound water/free water of all treatments was increased,and the difference was significantly compared with the CK.The bound water/free water of A2 treatment was 58.6% higher than that of the CK in November and 332% higher than that of the CK in December.2.The relative conductivity,malondialdehyde content and LT50 of leaves and branches were significantly effected in Zelkova schneideriana treated by different concentrations of exogenous CaCl₂.Different treatments have slowed down the growth trend of the two indicators.The A2 treatment showed the largest decrease compared with the CK.The leaf LT50 and shoot LT50 of A2 treatment were-10.6 °C and-10.09 °C respectively.3.The soluble protein,soluble sugar,chlorophyll content and SOD activity in leaves and branches were significantly effected in Zelkova schneideriana treated by different concentrations of exogenous CaCl₂.The contents of soluble protein and soluble sugar were increased,and the chlorophyll content was decreased,the activity of SOD was increased by different treatments.The difference of each index was significantly compared with the CK.4.The diameter,area and density of the vessel was significantly reduced by different concentration of exogenous CaCl₂.Compared with the CK,A2 treatment was the largest decreased in temperature.The diameter,area and density of branches treated with 20 mmol/L CaCl₂ in December were 15.8%,25.3% and27% smaller than that of the CK.5.The stomata morphology was significantly effected in Zelkova schneideriana treated by different concentrations of exogenous CaCl₂.The closing degree of stomata was slowed down and the stomata density was reduced in all treatments,and the difference was significantly compared with the CK.In November,the stomata opening of A2 treatment was 21.5% higher and the stomata density was 13.6%lower than the CK.6.The shoot germination rate was significantly effected in Zelkova schneideriana treated by different concentrations of exogenous CaCl₂.The shoot germination rate of all treatments was higher than that of the CK,The shoot germination rate of A2 treatment was 13.13%.7.The comprehensive evaluation of the cold resistance was ranked as A2 > A1 > A3 > A4 > CK in Zelkova schneideriana treated with different concentration of exogenous CaCl₂,and the average subjection degree of A2 was the biggest,and the treatment of 20 mmol/L CaCl₂ was the best for improving the cold resistance of Zelkova schneideriana.