Physiological Response of Potted Tomatoes to NaCl and Na2SO4 Brackish Water Irrigation
[Objective]Brackish water irrigation is one of the important means to increase irrigation water sources and to alleviate the shortage of agricultural water in arid areas.However,unreasonable irrigation water quality can severely limit the physiological activity and growth of plants.Carrying out research on the effects of different salt types of brackish water irrigation on the physiological changes of tomato leaves is conducive to reveal the mechanisms of salt tolerance to different types of salt in the salt-sensitive crop tomato at the physiological level,which is of great significance to agricultural production as well as to the use of brackish water for water conservation and salt control.[Method]In this study,tomato was used as an object of study in a brackish water irrigation pot experiment,and the two factors of irrigation water salt type(NaCl(T1)and Na2SO4(T2))and salinity(0,1.5(S1),3.0(S2),4.5(S3)and 6.0(S4)dS·m-1)were set to analyze the changes of physiological indexes,such as leaf gas exchange parameters,osmotic and antioxidant physiological regulation,and ionic balance,in tomato plants subjected to different types and degrees of stress at different reproductive periods.The reasons for the differences in the degree of decline in photosynthetic capacity of tomato under NaCl and Na2SO4 stress were explored too.[Result]Brackish water irrigation caused significant decreases in leaf net photosynthetic rate(Pn),stomatal conductance(Gs),and transpiration rate(Tr)in the late stage of fertility(mature picking stage)and high salinity(S4)treatments compared with CK,and the contents of proline(pro),soluble sugar(SS),malondialdehyde(MDA),and leaf Na+ increased continuously during the salt stress and the progression of the fertility period(P＜0.05).The superoxide dismutase activity(SOD)showed a trend of increasing and then decreasing with increasing salinity in the late reproductive stage.The highest decreases in Pn,Gs,and Tr could be up to 44.13%,64.53%,and 33.75%,respectively,whereas the increases in pro,SS,MDA,and Na+ could be up to 2.31,0.77,0.55,and 5.81 times higher than that of CK,respectively,all of which achieved under T1 stress.The correlations of SS,SOD and K+/Na+ with Pn were significantly changed under the two salt stresses,in which the slopes of the regression lines of SS and Pn were significantly higher under T1 treatment than T2(P＜0.05),the slopes of the regression lines of SOD and Pn were significantly lower under T1 treatment than T2(P＜0.05),and the regression curves of K+/Na+ and Pn showed that the T1 curves were relatively leftward.The results of principal component analysis showed that,under T1 treatment,SOD activity value was higher,which had an important role in Pn stabilization,but it was suppressed in the late reproductive stage,and could only enhance the water use efficiency to a certain extent;under T2 treatment,the physiological indexes were less stressed,in which the SS accumulation was related to the photosynthetic products,which could promote the biomass accumulation.[Conclusion]Salt stress led to excessive Na+ absorption by leaves,causing a decrease in net photosynthetic rate,stomatal conductance and transpiration rate of tomato,and the accumulation of malondialdehyde in leaves,while leaves increased superoxide dismutase activity as well as proline and soluble sugar content to cope with the stress.Under the same irrigation salinity,the net photosynthetic rate and stomatal conductance of tomato leaves were more affected by NaCl stress,soluble sugars maintained the stability of net photosynthetic rate under Na2SO4 stress,superoxide dismutase was able to protect the photosynthetic system under NaCl stress,and the NaCl treatment was required to maintain a higher leaf K+/Na+ level when the net photosynthetic rate was the same.Tomato leaves under Na2SO4 stress were less affected by stress,whereas tomato under NaCl stress had higher water use efficiency at the same salinity.The recommended salinity for irrigation of brackish water containing mainly NaCl was less than 3 dS·m-1,and the salinity for irrigation of brackish water containing mainly Na2SO4 was not more than 4.5 dS·m-1.
tomatobrackish water irrigationsodium stressphotosynthesisplant physiology
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