Effect Of NaCl Stress On The Photosynthetic Characteristics And Nitrogen Metabolism Of Sour Jujube Seedlings

【Object】To explore the influence of NaCl stress on sour jujube seedling photosynthetic and chlorophyll fluorescence characteristics nitrogen metabolism,provide reference for salt tolerance mechanism of zizyphus jujube.【 Method 】 A hydroponic experiment was conducted to study the effects of different Na Cl concentrations(0,50,100,150 and 200 mmol·L-1)on the Net photosynthetic rate(Pn)Net stomatal conductance(Gs),Transpiration rate(Tr),Intercellular CO2 concentration(Ci),the maximum fluorescence yield(Fm),the maximal photochemical efficiency of photosysteⅡ(Fv/Fm),photosynthetic electron transport rate(ETR),the photochemical quenching coefficient(qP),the initial fluorescence yield(F0),non photochemical quenching coefficient(NPQ)of photosynthetic and chlorophyll fluorescence characteristics of sour jujube seedlings and nitrate reductase(NR)activity,glutamate synthase(GOGAT)activity,glutamine synthetase(GS)activity,NO3--N,free amino acid concentration,and chlorophyll concentration in roots,stems,and leaves of sour jujube.【Result】1.The results showed that compared with the control,NaCl reduced Pn,Gs,Tr,Fm.The chlorophyll-fluorescence parameters showed that NaCl reduced Fv/Fm,ETR,qP.In contrast,NaCl increased F0 and NPQ.Ci decreased and then increased as both Na Cl and time increased.The values of Pn,GS,Tr,Fm,Fv/Fm,ETR,qP,Fo,NPQ,and Ci increased in the order 200mmol·L-1 < 150 mmol·L-1 < 100 mmol·L-1 < 50 mmol·L-1.2.The results showed that NaCl significantly reduced NR activity in jujube roots and stems compared with the control.The 150 and 200 mmol?L-1NaCl treatments significantly reduced NR activity in jujube leaves.The GS activity in roots and leaves and the GOGAT activity in stems and leaves were significantly lower in the control than in the NaCl treatments.The 150 and 200mmol?L-1 Na Cl treatments significantly reduced GS activity in stems and GOGAT activity in roots.The 150 and 200 mmol?L-1 NaCl treatments significantly reduced NO3--N concentrations in jujube roots.The NO3--N concentration in stems and leaves increased and then decreased as Na Cl increased.Free amino acid concentrations increased significantly in jujube roots,stems,and leaves as NaCl increased.In contrast,stem chlorophyll concentrations significantly declined as NaCl increased.The 100,150,and 200 mmol?L-1 NaCl treatments significantly reduced chlorophyll concentrations in jujube roots and leaves.【Conclusion】1.Low concentration of Na Cl(50 mmol?L-1)under the treatment of wild jujube photosynthesis decline is the stomatal limitation;the high concentration of NaCl(100 mmol ?L-1-200 mmol ? L-1)under the treatment of wild jujube photosynthesis decline is non stomatal limitation.Furthermore,NaCl damage to the PS II reaction center decreased primary capture capacity and the photosynthetic electron transport rate.2.In summary,high Na Cl concentrations(i.e.,150 and 200 mmol ? L-1)reduced NR activity,GOGAT activity,GS activity,NO3--N concentrations,and chlorophyll concentrations in jujube roots,stems,and leaves.In contrast,high Na Cl concentrations increased free amino acid concentrations.The decrease in NR activity weakened the reduction of NO3--N.The NaCl stress reduced the activities of both GOGAT and GS activity,thus hindering the operation of the GS /GOGAT cycle.This reduced the assimilation of NH4+ in the GS/GOGAT cycle,causing N metabolism to decline.