Physiological And Biochemical Responses Of The New Cultivar Of Zelkova Schneideriana ’Hentiangao’ Under Saline-alkalinity Stress

Zelkova schneideriana’Hentiangao’is a new cultivar of Zelkova schneideriana Hand.-Mazz, which was selected from seedings.’Hentiangao’belongs to small deciduous trees or shrubs, which has the characteristics of good ornamental value and strong resistance. The purposes of the study were to explore the salt-tolerance of’Hentiangao’ and provide basis for its popularization and application on saline and alkali land. The experimental subjects are one-year grafted seedling of’Hentiangao’. Through the artificial simulation of saline-alkali stress, the research set three different types of stress. The stresses were NaCl stress, NaHCO₃ stress,NaCl and NaHCO₃ stress mixed with the mole one to one,which was named as A, B and C respectively, and each type set CK,50mmol/L, 100mmol/L,200mmol/L,400mmol/L totally five concentration gradients to process. The varieties of 12 growth indicators and physiological and biochemical indicators of’Hentiangao’under salie-alkali stress were measured for determining the differences of the stress tolerance to different salts and the stress tolerance ranges to the same salt and filtering proper index for evaluating the salinity-resistance of’Hentiangao’, These indicators were salt injury index,survival rate, plant height growth, relative electrical conductivity, malondialdehyde, superoxide dismutase, peroxidase, proline, chlorophyll, chlorophyll a and chlorophyll b and carotenoids. The changes of photosynthetic parameters and chlorophyll fluorescence parameters of’Hentiangao’ seedlings at different salt concentration were also tested. The concentrations were CK、 50mmol/L,100mmol/L,200mmol/L and 400mmol/L.After this, it discussed the response mechanism of’hentiangao’to salt stress. The main results are as followings:（1） salie-alkali stress had significant influence on the leaf morphological of ’Hentiangao’. Salt injuries appeared in mature leaves firstly followed by new leaves. The salt injuries of mature leaves of the plant showed that the edge or tip of leaves appeared shriveled firstly, then turned yellow and fell leaves. In the end, the branches turned black, then died. The plants of salt injury degree and response rate were different under three different types of salie-alkali stress treatment. The salt injury index and salt levels of the leaves of’Hentiangao’increased as the stress concentration and stress time continued. The salt injury index of’Hentiangao’under different stress with the same concentration showed that group C was the largest, then was the group A, group B was the minimum. ’Hentiangao’response to NaCl salt stress and mixed salie-alkali stress earlier（2） Both the growth indexes and physiological and biochemical indexes of ’Hentiangao’were changed under salie-alkali stress.The survival rate of’Hentiangao’ seedlings under salie-alkali stress was on the decline along with the increasing of stress concentration. It characterized by B≥A≥C under stress of the three groups. According to quantity theory in death,the lethal concentration caused half death of ’Hentinagao’ under NaCl, NaHCO₃, NaCl and NaHCO₃ moore hybrid stress were between in 200mmol/L to 400mmol/L. It showed inhibitory effect on the growth of ’Hentiangao’ seedlings under salie-alkali stress. The inhibitory effect of group C was the largest, second group A, group B was minimal. Rec,MDA and Pro showed the trend of rising as the stress concentration and stress time continued. SOD,POD, Chlorophyll and Chlorophyll a showed the trend of rising first and then downward. The trend of chlorophyll b and Carotenoid were different for different types of stress and stress concentration. Different stresses on all the physiological and biochemical indexes of ’Hentiangao’ showed a similar changing process.（3） The results using principal component analysis combined with the membership function of comprehensive evaluation showed that the tolerance order of ’Henitiangao’ for three types of stress from strong to weak was NaHCO₃ stress> NaCl stress>stress of NaCl and NaHCO₃ moore mixed stress. The following 4 indexes:Chlorophyll,chlorophyll a, SOD and POD activity can be used as the salt-tolerance identification indicators of ’Hentiangao’.（4） The light response curves of the blade of ’Hentiangao’ under different concentration of NaCl stress were quadratic curves.The photosynthesis of ’Hentiangao’ was restrained significantly under NaCl stress. With the stress concentration and stress time continued, the net photosynthetic rate of ’Hentiangao’ decreased due to the affects of non-stomatal limitation of photosynthesis. It also showed that salt stress reduced the light environment adaptability and the ability to light energy utilization of ’Hentiangao’. In the meantime, the salt stress abated the photo chemical reaction. It also reduced the energy absorption ability and decreased the electron transfer rate. That affected light energy into chemical energy and influenced the photosynthesis. ’Hentiangao’ under salt stress can avoid or alleviate oxidative damages by increasing heat dissipation to burn off excess light energy.