Effects Of Heterogeneity Of Soil Salt On Growth Physiology And Rhizosphere Soil Characteristics Of Cucumber

As one of the main abiotic stresses,the growth of plant often has been severely affected by salt stress.High salt stress will inhibit plant growth by damaging the physiological and metabolism of plants.At present,most of the study on salt tolerance of plants has focused on homogeneous salt stress,but in agricultural production,the roots of plants are normally distributed in soil with uneven salinity.It helps to understand the salt tolerance mechanism of plants,and provide a theoretical basis for crop stress resistance cultivation and breeding of new salt-tolerant varieties by exploring the physiological response of plants to heterogeneous salt stress and the change of rhizosphere soil environment.In our study,the salt-sensitive variety ‘Jinyou No.1’ was treated with different concentrations of salt solutions by establishing a root-dividing system to study(1)cucumber physiology response to heterogeneous salinity;(2)relationship between cucumber growth and different salt concentration of root region in heterogeneous salinity;(3)differences of physicochemical properties of cucumber rhizosphere soil under heterogeneous salinity;(4)effects of rhizosphere microbial community structure of cucumber by heterogeneous salinity.The main results were as follows:1.Compared with homogeneous salinity,the root length,root volume,root surface area and root tip number of non-or low-salt side of inhomogeneous salinity were markedly higher than homogeneous salinity with the same total salt concentration,which promoted the water uptake of the low-salt side,of which 62.40%-88.47% of water uptake was from the low-salt side.At the same time,the extension of shoot,leaf area and total biomass were also significantly increased,and the MDA content,proline and soluble sugar content in cucumber leaves increased less,which indicated that stress effect of non-homogeneous salinity on cucumber was lower than homogeneous salinity in hydroponic experiment.However,with the increase of salt concentration in the low salt side of inhomogeneous salinity,difference in these treatments was gradually reduced.The mitigation effect of heterogeneous salinity disappeared when salt concentration of low-salt side reached a certain threshold.Regression analysis of the growth physiological indicators of cucumber under inhomogeneous salt stress treatment with the salt concentration in the root zone under homogeneous and inhomogeneous salt stress revealed that the highest correlation was found between the growth of cucumber and the root-weighted mean salinity concentration.2.In soil culture experiment,chlorophyll content and fluorescence parameters Fv/Fm,Fv/Fo,Y(Ⅱ),ETR,NPQ and q P were significantly affected by salt stress.Chlorophyll content,Fv/Fm,Fv/Fo,Y(Ⅱ),ETR and q P under non-homogeneous salinity were higher than homogeneous salinity,and cucumber biomass was also significantly increased,which indicated that the impact of inhomogeneous salinity on conversion efficiency of light energy of cucumber was less than homogeneous salinity.3.In soil culture experiment,osmotic adjustment substance and MDA content had smaller increase in roots of low salt side of inhomogeneous salinity compared with high salt side and homogeneous salinity.There was no significant difference in urease activity and catalase activity in low salt side of inhomogeneous salinity compare with control,sucrase activity was lower than control,but three enzymes activities of low salt side were significantly higher than homogeneous salinity,which indicated that cucumber can get less injuries than homogeneous salinity in non-homogeneous salinity.4.The results of 16 S rRNA sequencing of different rhizosphere soil samples in the soil culture split-root salt stress test showed that different salt stress treatments had a small effect on the total abundance of bacterial communities,but significantly reduced the diversity of bacterial communities.The bacterial community composition showed significant variability in different rhizosphere soils,with the Proteobacteria being the dominant phylum in cucumber rhizosphere soils,accounting for 59.03%-70.06% of the total abundance.The bacterial abundance of some Acidobacteria,Proteobacteria,Chloroflexi and Actinobacteria was significantly higher in the control than in the salt stress treatment;the relative abundance of bacteria of most Cyanobacteria,Actinobacteria and Proteobacteria increased in the homogeneous salt stress treatment;in the inhomogeneous salt stress,most of the bacterial abundance of Proteobacteria and Bacteroidetes that increased in the high salt side also increased in the low salt side,and the abundance was greater in both the control and homogeneous salt stress treatments.In addition,the bacterial abundance of some Proteobacteria and Gemmatimonadetes also increased in the low-salt side of inhomogeneous salt stress.