Effects Of Saline-alkaline Stress On Physiological And Biochemical Characteristics Of Xanthoceras Sorbifolia Seedings

In recent years,the problem of soil salinization and heavy metal pollution has become the hotspot of soil environmental management and research.Due to the development of modern industry,the discharge of waste water and exhaust,and the extensive use of chemical pesticides,resulting in the heavy metal ions in the soil have increased dramatically.The heavy metal ions in various heavy metal salts not only reduces the soil fertility,but also affect the normal growth of plants,and reduce the yield and quality of crops.Soil salinization is caused by the accumulation of soluble salts,containing more soluble neutral salt,pH value of not more than 8.5 of the soil called saline soil,containing more soluble alkaline salt,pH greater than 8.5 Soil is called alkaline soil.In nature,saline and alkaline soils often exist simultaneously,the common effect caused saline-alkaline stress.Xanthoceras sorbifolia,widely distributed in the Northeast China,North China and Xinjiang area,is a kind of unique woody oil plants in north China.Xanthoceras sorbifolia has strong environmental adaptability,its high soil fertility,cold resistant,drought resistant,and aeolian resistant characteristics make it become the preferred oil and ecological economic tree species for mountain afforestation,returning farmland to forest,windbreak and sand fixation,and it is also listed as one of the eight species of biodiesel manufacturing in 11th "Five-Year" development plan.With the increase of energy demand,Xanthoceras sorbifolia is extended to soil depletion areas such as Xinjiang,saline-alkaline and heavy metals have seriously affected the soil composition in these area,leading to varying degrees of plants growth,such as photosynthetic rate,chlorophyll content,enzyme activity,osmotic regulating substances etc..The changes and trends of physiological and biochemical characteristics of Xanthoceras sorbifolia were studied under saline-alkaline and heavy metals stress in this paper,it is great theoretical and practical significance to the in-depth study of Xanthoceras sorbifolia adaptation to environment stress and rational popularization.In this study,two months of Xanthoceras sorbifolia seedlings were selected as the research object,and the stress experiment of saline-alkaline and heavy metals was carried out.According to the pollution situation of heavy metals in groundwater in the typical areas of southern Xinjiang,two typical heavy metals,Fe and Mn,were selected with NaCl and Na2CO3 to carry out complex saline-alkaline and heavy metals stress tests.Test settings CK group as the control group,the concentrations of FeSO4(group A),FeSO4+ MnSO4(group B),saline-alkaline + FeSO4+ MnSO4(group C)were set to 3 times,and each experiment was repeated three times,that is,each stress concentration under a total 9 tests.On the first day,third day and fifth day after the stress treatment,the experimental data were measured in CK group,group A,group B,and group C respectively.The measurement results are as follows:1.Changes in the activity of SOD and POD in the leaves of Xanthoceras sorbifolia were consistent with saline-alkaline and heavy metals stress.In general,with the intensification of the stress concentration and the prolongation of the stress time,SOD and POD were increasing,both were higher than the CK group values in the group C,and reached the maximum.It can be concluded that Xanthoceras sorbifolia can enhance the activity of antioxidant enzyme in plants under saline-alkaline and heavy metals stress,and the change trend of MDA content coincided with the change of active enzyme,indicating that antioxidant enzyme played a major role in scavenging reactive oxygen,reduced the lipid peroxidation of cell membranes,but once the stress beyond the tolerance limit of Xanthoceras sorbifolia,enzyme activity would be reduced,once again leaded to a large number of MDA production.2.The content of MDA in the leaves of Xanthoceras sorbifolia was significantly affected by saline-alkaline and heavy metals stress.Under the general trend,the content of MDA was increased slowly with the increasing of the stress concentration and stress time below saline-alkaline and heavy metals stress,and reached the maximum with the Fe+ Mn +saline-alkaline stress.MDA reflects the degree of membrane lipid peroxidation,and the increasing of MDA content in plant leaves leads to the accumulation of reactive oxygen species in plant cells,and severe peroxidation of cell membrane.3.With the increasing of saline-alkaline and heavy metals stress and the time prolonged,the contents of proline and soluble protein in the leaves of Xanthoceras sorbifolia were increasing,and the differences between the stress groups increased.Group C reached the maximum.It can be seen that osmotic regulation substances in leaves was significantly affected by saline-alkaline and heavy metals stress.With the increasing of stress,the plant accumulated proline and soluble protein content to remove reactive oxygen species and decreased membrane lipid peroxidation.4.The electrical conductivity of Xanthoceras sorbifolia leaves was significantly changed under saline-alkaline and heavy metals stress,with the increasing of the stress concentration and the prolonging of the stress time,the conductivity showed the upward trend,the conductivity of Xanthoceras Sorbifolia leaves reached the maximum with group C in different days.The results showed that the structure of the plant biofilm had a destructive change under saline-alkaline and heavy metals stress,the loss of braking ability of the plant biofilm,and the permeability of the cell membrane became larger,and the conductivity increased.5.The contents of chlorophyll a,chlorophyll b,total chlorophyll and carotenoid in the leaves of Xanthoceras sorbifolia were significantly affected by saline-alkaline and heavy metals stress in the same trend,the first day and third day after stress treatment showed increasing at first and then decreasing,all the highest content in the first day of group A,the decline trend in the stress fifth day,the chlorophyll content was lower than CK group.6.The photosynthesis of Xanthoceras Sorbifolia leaves was inhibited by saline-alkaline and heavy metals stress,i.e.,Pn,Gs,Ci and Tr of Xanthoceras sorbifolia leaves decreased gradually with the enhancement of saline-alkaline and heavy metals stress,which may be related to the increase of the concentration of free Ca2+-in defending cytoplasm caused by saline-alkaline and heavy metals stress,causing stomatal closure and decreasing of Pn,Ci and Tr.