Physiological Response Of Hollies To Salt Stress And The Selection Of Salt-tolerant Species

Considering the issue of developing and utilizing green ecology along the beach,we collected 13 species of Ilex?hollies?materials,studied their growth and physiological changes under different salt stress conditions,and screened out salt-tolerant holly species by observing the symptoms of salt damage.Aimed to provide a theoretical basis for the selection of salt-tolerant tree species in saline-alkali land in northern Jiangsu,the growth and physiological indicators of salt-tolerant hollies and sensitive hollies were measured,including plant height growth,dry weight of root,stem,and leaves,biomass,seedling growth rate,root-to-shoot ratio,changes in root structure and other growth indicators,chlorophyll content,photosynthesis indicators,chlorophyll fluorescence parameters,membrane system,enzyme system,organic osmotic adjustment substance content,and other physiological indicators.The main points of this current study were summarized as follows:1.The salt tolerance of evergreen hollies is significantly higher than that of deciduous hollies.Through salt stress screening,deciduous holly species can be divided into three different levels of salt sensitivity:mildly sensitive:I.decidua‘Sentry';moderately sensitive:I.verticillata‘Gray';highly sensitive:I.verticillata‘Oosterwijk',I.verticillata‘Winter Red',I.verticillata‘Winter Gold',and I.micrococca.Divide evergreen hollies into three different levels of salt tolerance:mildly salt-tolerant:I.dabieshanensis,I.‘Nellie R.Stevens',and I.cornuta'Fortunei';moderately salt-tolerant:I.cornuta‘Dwarf Burford'and I.‘Sunny Fosteri';highly salt-tolerant:I.×koehneana‘Emily Bruner'and I.salicina.2.The effect of salt stress treatment on the growth and morphology of hollies:With the increase of the concentration of salt stress,the relative growth of I.decidua‘Sentry'and I.×koehneana‘Emily Bruner'gradually decreased,and the ratio of root and shoot of I.verticillata‘Gray'and I.dabieshanensis gradually decreased.The root-to-shoot ratio of I.decidua‘Sentry'and I.×koehneana‘Emily Bruner'rose first and then declined,and the biomass of all tested tree species showed a trend of first increasing and then decreasing.3.Effect of salt stress treatment on physiological indexes of chlorophyll and photosynthetic factors in hollies:With the increase of salt stress time,the chlorophyll a,chlorophyll b,total chlorophyll content,chlorophyll fluorescence parameters,net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration,and transpiration rate basically showed a downward trend.4.The effect of salt stress on the holly membrane system:Under salt stress treatment,the membrane permeability and malondialdehyde content of each holly tested increased.I.verticillata‘Gray''s membrane permeability and malondialdehyde content increased by a large amount.I.dabieshanensis and I.×koehneana‘Emily Bruner''s membrane systems were not greatly affected.Therefore,the physiological indicators of the membrane system can be used to quickly screen holly species for salt-tolerant species and sensitive species.5.Effects of salt stress on osmotic adjustment substances of hollies:Under salt stress,the soluble sugar content of the tested tree species increased compared with the control.All tested tree species showed an increase in soluble protein and then a decrease in proline content,and a gradual increase in proline content.There was no significant difference between salt-tolerant and sensitive holly species.6.The effect of salt stress on the holly enzyme system:With the increase of salt stress time,the SOD activity of I.decidua‘Sentry',I.dabieshanensis and I.×koehneana‘Emily Bruner'all increased rapidly.The CAT activity of tested tree species shows a tendency to rise rapidly in the middle of salt stress and decrease in the later period of salt stress.7.Effect of salt stress on root structure:Salt stress has a significant effect on the root structure of deciduous hollies,but short-term salt stress will not have a significant effect on evergreen hollies.Most evergreen holly varieties can be used as excellent salt-tolerant ornamental materials for cultivation in saline-alkali areas.Physiological indicators such as growth,chlorophyll fluorescence parameters,net photosynthetic rate,stomatal conductance,transpiration rate,soluble protein,proline and CAT activity for deciduous hollies and evergreen hollies all responded to salt stress,and the response in root structure change is inconsistent.The relative growth of plant height,root-to-root ratio,chlorophyll fluorescence parameters,membrane permeability,malondialdehyde,soluble sugar and SOD activity of low-sensitivity deciduous hollies and high-salt-tolerant evergreen hollies are consistent in response to salt stress,and are highly sensitive.The responses of highly sensitive deciduous hollies and low salt-tolerant evergreen hollies to root-to-root ratio and chlorophyll fluorescence parameters were consistent with salt stress.In deciduous hollies,intercellular CO₂ concentration,membrane permeability,malondialdehyde content,soluble sugar,SOD activity,and POD activity have different response rules to salt stress.Membrane permeability and malondialdehyde content can be used as the most effective index for screening deciduous hollies salt-tolerant materials.The soluble sugar content of evergreen hollies is inconsistent in response to salt stress,and can be used as an effective index for screening evergreen hollies salt-tolerant materials.