| Exploring the physiological and biochemical indicators of garden plants is of great guiding significance for the selection and application of tree species in urban garden environment.In recent years,the heavy use of snow melting agents in northern cities in winter has caused significant damage to garden plants.As an essential nutrient element for plant growth and development,calcium plays a key role in the process of plant flower induction,flower bud differentiation and flowering regulation.Therefore,this research takes annual Salix matsudana f.pendula Shneid.seedlings as the research object and conducts the experiment by hydroponic culture,setting 3 sodium chloride concentration levels(0,50,200mmol·L-1)and 5 different calcium gradients(0,100,200,400,800 mg?kg-1).Then obtain the most suitable calcium gradient for S.matsudana seedlings under the influence of sodium chloride through the determination and analysis of growth,photosynthetic indicators,chlorophyll fluorescence,water use efficiency and enzyme activity of S.matsudana seedlings.The purpose of this research is to provide a theoretical basis for alleviating the adverse effects of excessive salt on S.matsudana after using snow melting agent through the application of exogenous calcium.The research results are as follows:（1）The application of exogenous calcium has a significant promotion effect on the growth of S.matsudana seedlings under sodium chloride stress（p<0.05）.The biomass of each part of S.matsudana seedlings,the plant height,and basal stem growth are obvious（p<0.05）.The optimum calcium concentration for S.matsudana growth is 400 mg·kg-1.Using too high or too low calcium concentration treatment level makes S.matsudana The long increment was significantly reduced（p<0.05）.（2）The application of exogenous calcium to S.matsudana seedlings under salt stress significantly raised the photosynthetic parameters（net photosynthetic rate,stomatal conductance,transpiration rate）（p<0.05）,and the photosynthetic pigments（chlorophyll and carotenoid）.The synthesis and accumulation also improved with the application of exogenous calcium,and the synthesis and accumulation of soluble sugar,starch and soluble protein in S.matsudana also showed significant changes.At calcium concentration treatment level of 400mg?kg-1,the photosynthetic parameters,photosynthetic pigments and photosynthetic products of S.matsudana seedlings reached the optimal values,and calcium deficiency or excessive calcium concentration did not show the best effect on alleviating the photosynthesis of plants under salt stress.（3）The chlorophyll fluorescence of S.matsudana seedlings is greatly affected by the addition of exogenous calcium.According to the analysis of their chlorophyll fluorescence parameters（Fv/Fm,Fv/Fo）,the values of Fv/Fm and Fv/Fo of S.matsudana seedlings increased significantly,and the peak value appeared when the concentration of exogenous calcium reached 400 mg·kg-1,significantly higher than other calcium concentration levels（p<0.05）.As the calcium concentration continues to increase,exogenous calcium stresses the chlorophyll fluorescence of S.matsudana seedlings.（4）The instantaneous water use efficiency of S.matsudana reaches its peak when the exogenous calcium concentration is 400 mg?kg-1treatment level,which is significantly better than other calcium gradient treatments（p<0.05）.After receiving salt stress,its long-term water use efficiency remarkably increased after applying exogenous calcium and calcium,and had the best improvement effect when the exogenous calcium concentration was 400mg·kg-1（p<0.05）.（5）By measuring POD,SOD,CAT of S.matsudana seedlings under different exogenous calcium concentrations,it can be found that when the exogenous calcium concentration is400 mg·kg-1,the various stress resistance indicators of S.matsudana reach the optimal value,and relatively better than the treatment with higher or lower concentration.It can be seen that when the exogenous calcium concentration is 400 mg·kg-1,calcium has the most obvious effect on alleviating salt stress in S.matsudana and improving its stress resistance against uncomfortable environment.Based on the above results,the optimum concentration of exogenous calcium for the growth and development of S.matsudana seedlings is 400 mg·kg-1.Excessively high or low exogenous calcium concentration has not achieved the excellent effect of alleviating the salt stress of S.matsudana. |
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