Alleviating Effect Of Exogenous ALA On Siberian Nitraria Salt Stress

Nitraria sibirica Pall.is a strong xerophytic shrub and halophyte of the Nitraria genus Nitraria.It has strong salt tolerance and is an excellent tree species for controlling land salinization.This experiment uses S.sibirica seedlings as test materials to investigate the different levels(0 mg·L-1,30 mg·L-1,60 mg·L-1)of exogenous 5-aminolevulinic acid(ALA)applied to different levels of Siberian Nitraria(0 mmol·L-1,200 mmol·L-1,400 mmol·L-1).In order to reveal the mitigation effect and mechanism of 5-aminolevulinic acid(ALA)on Nitraria under salt stress.The following conclusions were reached:(1)The relative water content of Siberian Nitraria leaves will increase first and then decrease with the increase of NaCl concentration.When the NaCl concentration was 200 mmol·L^-1,the relative water content rises to the highest level,and as the NaCl concentration continues to increase,the relative water content will decrease.After applying a certain concentration of ALA,the relative water content of the leaves increased,and the water loss of the leaves was alleviated,and 30 mg·L^-1 ALA had the best relief effect.(2)The content of malondialdehyde(MDA)in the leaves of Siberian Nitraria were decreased early then increased with increasing concentration of NaCl concentration,and were minimum level at 200 mmol·L^-1NaCl.and then increased slightly.High concentration of MDA can cause membrane lipid peroxidation and damage cell membranes.Applying a certain concentration of ALA relieves this phenomenon and reduces cell membrane damage.where in 30 mg·L^-1 ALA has the best relief effect.(3)With the increase of NaCl concentration,the content of endogenous ALA as the starting material of chlorophyll synthesis pathway and intermediate products uroporphyrinogen?(Uro?),protoporphyrin?(Proto?),magnesium-protoporphyrin?(Mg-Proto?),prochlorophyllate(Pchlide)content and chlorophyll(chlorophyll)content all were increased early then decreased.The addition of exogenous ALA,the content of each index rose and had a significant promotion effect.where in 30 mg·L^-1 ALA has the most obvious promotion effect.(4)With the increase of NaCl concentration,the gas exchange parameters of Siberian Nitraria were significantly affected,which showed that the net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)were increased early then decreased and the intercellular CO2 concentration Ci)first descends and then rises.Applying a certain concentration of ALA can effectively relieve,increase Pn,Gs and Tr,and significantly reduce Ci.where in 30 mg·L^-1 ALA has the best treatment effect,indicating that a certain concentration of ALA can promote leaf stomatal opening and increase photosynthetic efficiency.However,too high concentration of ALA(60 mg·L^-1)will have a negative effect.(5)With the increase of NaCl concentration,Siberian Nitraria chlorophyll fluorescence parameters are affected to varying degrees,showing that various indicators change correspondingly with the increase of NaCl concentration.At low Na C l concentration(?200mmol·L^-1),the maximum photochemical efficiency and actual photochemical efficiency of Siberian Nitraria increased with the increase of NaCl concentration,while at high NaCl concentration(?200 mmol·L^-1),the downward trend,the photochemical quenching coefficient and the apparent electron transfer efficiency generally increase first and then decrease with the increase of NaCl concentration,and all reach the maximum when the NaCl concentration is 200mmol·L^-1,rather than photochemical quenching.The coefficient(NPQ)is the opposite,It increases first and then increases with increasing NaCl concentration.The application of a certain concentration of ALA can play a alleviation effect,promote Fv/Fm,?PSII,q P,ETR,inhibit NPQ,and all have the best effect when the ALA concentration is 30 mg·L^-1.It shows that a certain concentration of ALA can effectively improve the photochemical efficiency of plants and slow down the photosuppression caused by salt stress.