Effects Of Salinity And Drought Interaction On Physiological Characteristics Of E.Moorcroftii Seedlings

Nowadays, the aggravation of soil salinization poses great threats to the ecological security and agriculture sustainability. The soil of the Yellow River Delta in China is seriously salinized, the growth of crops inhibited by salizition and drought because there is a lot of precipitation in summer and in spring rainfall is comparative dispersed, which reduce agricultural production and limit economic development.Elaeagnus angustifolia L is deciduous tree belonging to Elaeagnaceae Elaeagus, which is widely distributed in Northwest areas of China. It is able to grow healthily under high temperature, drought, salinization and other adversitys, it is known as the important species because of its ecological and economic benefits. The study on stress tolerance of Elaeagnus focus on single stress factor, there is few studies on salinity and drought interaction. In this paper, we studied the effect of salt and drought interaction on E. moorcroftii seedlings in order to provide foundation for introducing E. angustifolia into the Yellow River Delta. The results were summarized as following:1. Effects of salinity and drought interaction on growth characteristics of E. moorcroftii seedlings. The shoot and root biomass of E. moorcroftii seedlings increasingly decreased with the drought degree increasing under all kinds of treatments. There was no significant difference of the growth of seedlings between under 0.5% NaCl and light water stress interaction and under 0.5% NaCl or light water stress. It means that to some extent E. moorcroftii seedlings acquired a certain drought resistant by 0.5% NaCl pretreatment.2. Effects of salinity and drought interaction on inorganic ions, organic solutes and secondary metabolite of the leaves of E. moorcroftii seedlings. The Na⁺ and Clcontent of shoots and roots had no significant change when the E. moorcroftii seedlings suffered drought. The Na⁺ and Cl^- content significantly increased with the increasing of soil water content. The shoots K⁺ content slightly increased under drought stress and roots K⁺ content had no change, K⁺ content reduced with the reducing of soil water content under 0.5% NaCl and drought interaction. There is no difference in ions content of seedlings between treated with 0.5% NaCl and 0.5+MS（0.5% NaCl ⁺ moderate drought stress）. The Na⁺/K⁺ of shoots and roots keep a relatively low level under drought stress, but it obviously increased under the treatment with salt and drought interaction. The proline contents and soluble sugar contents of the leaves of E. moorcroftii seedlings significantly increased under salt stress and drought stress. The leaves of organic solute increased under 0.5% NaCl and drought interaction treatment. The content of flavonoids and total polyphenol increased with the reducing of soil water content, and reached the maximum value treated with 0.5% NaCl and drought interaction.3. Effects of salinity and drought interaction on photosynthetic indexes and chlorophyll contents of leaves of E. moorcroftii seedlings. The net photosynthetic rate（Pn）, stomatal conductance（Gs） and intercellular CO₂ concentration（Ci） of leaves of E. moorcroftii seedlings reduced apparantly under 0.5% NaCl. Secondly, Ci, Pn and Gs decreased with the soil water content reduced, Under salt and moderate drought stress interaction（0.5+MS）, compared with treatment of 0.5% NaCl, Ci, Pn and Gs of leaves of E. moorcroftii seedlings didn’t decrease significantly, and Ci, Pn and Gs of leaves of E. moorcroftii seedlings reached the lowest level under 0.5+SS（0.5% NaCl ⁺ severe drought stress） treated. With the soil water content decreased, chlorophyll synthesis of E. moorcroftii seedlings blocked heavily, and chlorophyll content significantly decreased. Fv/Fm,ΦPSⅡand qP decreased with the soil water content reduced under treatment of different extent of drought, Under salt and drought interaction, Fv/Fm,ΦPSⅡand qP first rised up and then moved down with the soil water content reduced, E. moorcroftii seedlings showed cross-adaptation under 0.5+MS treated and the Fv/Fm,ΦPSⅡand qP of leaves of E. moorcroftii seedlings treated with 0.5+SS reduced the lowest.4. Effects of salinity and drought interaction on MDA content and enzyme activities leaves of E. moorcroftii seedlings. MDA content of leaves E. moorcroftii seedlings under salt stress is highter than that in CK and significantly increased with the soil water content reduced, to compared with 0.5% NaCl treatmen, MDA content of 0.5+MS treated decreased slightly, the treatment of 0.5+MS had the highest MDA contend. SOD and CAT activities raised with the soil water content decreased, under the treatment of 0.5+SS, SOD and CAT activities reached the highest level, compared with treatment of 0.5% NaCl, SOD and CAT activities of leaves of E. moorcroftii seedlings treated with 0.5+MS didn’t present some differences.5. Growth recovery of E. moorcroftii seedlings after re-watering: The fresh weight of shoots, roots and leaves water content of every treatment under moderate water stress had no significant difference compared with CK, Althought dry weight of shoots and roots increased after re-watering, to compare with CK, they still keep low level. Growth recovery results of every treatment under severe water stress didn’t reach CK level, All kinds of growth index under 0.5+SS treatment reduced the lowest level. Compared with MS, the E. moorcroftii seedlings treated with 0.5+MS grew better.