Evaluation Of Salt Tolerance And Physiological-biochemical Characteristics Of Three Forsythia Seedlings

In order to enrich the species of tree greening in the coastal saline-alkali area in Hebei Province,and expand the forestation area and landscaping range of Forsythia in the coastal saline-alkali area.With Forsythia mandschurica,F.suspense and F.intermelia 1-year-old seedlings as test materials,potted saline water was used to control soil salinity.The experiment was designed with five NaCl gradient levels,CK(0.103%),T1(0.2%),T2(0.3%),T3(0.4%),and T4(0.5%).The salt damage of Forsythia seedlings were observed and recorded regularly.Salt stress treatments of the second day,ninth day,sixteenth day and twenty-third day were used to sample and determined physiological indexes of leaves:water saturation deficit,cell membrane permeability,content of MDA,content of chlorophyll,content of soluble sugar,content of soluble protein,content of free praline,enzymatic activity and ion content.And comprehensive evaluation of salt resistance on three Forsythia plants by subordinate function values analysis.The main results were as follows:(1)The salt damage of potted seedlings showed that F.intermelia had the lightest salt damage.Which was grade 2 and about 1/2 of the tip and leaf margin was scorched.Followed by F.mandschurica,showing grade 3,most of the leaves have tip,leaf margin scorch and defoliation;F.suspense was the most seriously affected by salt,showing grade4,with branches withered and leaves falling until death.(2)With the intensification of NaCl stress,the water saturation deficit of the three species of Forsythia plants increased.On twenty-third day of salt stress,when the NaCl concentration was 0.5%,the water saturation deficit contents of F.mandschurica,F.suspense and F.intermelia were increased by 202.65%,320.94%and 249.26%,respectively,compared to the control.(3)Under salt stress,the relative electrical conductivity of three Forsythia plants showed an upward trend with the increase of salt concentration.The growth rate of F.suspense increased the most,followed by the F.mandschurica,and the F.intermelia increased the smallest.The content of MDA in leaves showed an upward trend.On twenty-third day of salt stress,when the NaCl concentration was 0.5%,the content of MDA in leaves was the highest.Compared with the control,F.mandschurica,F.suspense and F.intermelia increased by 57.24%,72.46%and 52.66%,respectively.(4)With the increase of salt stress,the total chlorophyll contents in leaves of three Forsythia plants decreased,chlorophyll a content decreased slightly,and chlorophyll b content decreased significantly.Among the three species of Forsythia,the decrease of total chlorophyll content and chlorophyll a content from large to small is in the order of F.suspense,F.intermelia and F.mandschurica.The decrease of chlorophyll b content from large to small is F.suspense,F.mandschurica and F.intermelia.The NaCl stress had the most serious effect on the chlorophyll content in leaves of F.suspense.(5)With the deepening of salt stress,on twenty-third day of salt stress,when the NaCl concentration was 0.5%,the content of soluble sugar in leaves of F.mandschurica,F.suspense and F.intermelia were increased by 125.10%,69.50%and 178.70%,respectively.The F.intermelia had the largest increase,followed by F.mandschurica and F.suspense.Under salt stress,the content of soluble protein in the leaves of F.mandschurica and F.suspense was fluctuating an upward trend.However,the content of soluble protein in the leaves of F.intermelia was increased first and then decreased.The content of free proline showed an upward trend,and the degree of increase from large to small was the following:F.intermelia,F.mandschurica and F.suspense.On twenty-third day of salt stress,when the NaCl concentration was 0.5%,they increased by 125.10%,69.50%and 178.70%increased respectively compared with the control.(6)During the whole salt stress,the activity of SOD in leaves of F.mandschurica and F.suspense was fluctuating an upward trend.The activity of SOD in the leaves of F.intermelia increased first and then rose.Under salt stress,the activity of POD in the leaves of F.mandschurica and F.intermelia showed an upward trend,and the activity of POD in the leaves of F.suspense showed a downward trend.(7)The results showed that,under salt stress,the contents of Na~+in leaves of three Forsythia plants increased significantly,while the content of K~+decreased significantly,and the content of Na~+/K~+showed an upward trend.With the increase of salt concentration,the content of Na~+increased significantly,and the content of Na~+/K~+increased.This indicated that the ionic balance of F.suspense was destroyed,the plant suffered salt damage.And the normal metabolic balance of plants was disturbed,resulting in the lack of nutrient elements in plants and the slower plant growth.(8)Through the comprehensive analysis of subordinate function method,it can be concluded that the salt resistance ability of three Forsythia plants from large to small was F.intermelia,F.mandschurica and F.suspense.It was consistent with the salt damage of three species of Forsythia.The results showed that the F.intermelia can survive when the soil has a NaCl concentration of 0.4%,and the growth is strong when the NaCl concentration of 0.3%.F.mandschurica can survive at a concentration of 0.3%NaCl in the soil.The North China F.suspense can survive at a concentration of 0.2%NaCl in the soil.