Effects of saline- alkali stress on photosynthetic and chlorophyll fluorescence characteristics of different grape rootstocks

Abstract: 【Objective】In order to detect the effects of salt and alkali stress on the development progress, chlorophyl content, photosynthetic and chlorophyl fluorescence characteristics of grape rootstocks and shed lights on the mechanisms of these effects, we investigated the reaction of photosynthetic and Chlorophyll fluorescence characteristics of six main rootstock varieties used in grape production,3309M, 5BB, 1103P, 420A, 5C and SO4 to salt and alkali stress, and finally provided reference for selection of rootstocks resistant to salt and alkali.【Methods】In our study, we grew various nursery trees of grape rootstock varieties in greenhouses until they reached 8 leaf stages. Then hydroponic cultivation methods were used to support these plant materials for growth. Two treatments were set up: control(modified Hoagland nutrient solution) and saline alkali stress(modified Hoagland nutrient solution + 50mmol·L^-1 NaCl + NaHCO3)(mixed according to the amount of substance 1∶1). During the experiment,the nutrient solution was continuously ventilated with an inflatable pump, the water lost in the hydroponic basin was supplemented to the 6 L scale mark every day, and the nutrient solution was replaced every 5 days. The new growth, chlorophyll content, photosynthetic characteristics and chlorophyl fluorescence parameters of different grape rootstocks were measured, and the principal component analysis was carried out.【Results】The salt and alkali stress had universally negative effects on all characteristics related to development progress, chlorophyll content, photosynthetic and chlorophyl fluorescence.Compared with the control, the growth of the shoots of each rootstock decreased, and the content of chlorophyll(Chl a, Chl b and Chl a+b) decreased as well. The decrease of Chl b content was less than Chl a, indicating that saline-alkali stress would affect the synthesis of chlorophyll, and Chl b was more sensitive to saline-alkali stress on 15 d after the treatment; The net photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2concentration(Ci) and transpiration rate(Tr) of the each rootstock also showed a downward trend, and the change of leaf Pnwas the same as that of Chl a+b content, indicating that the inhibition of rootstock plant photosynthesis was caused by stomatal factors, and the decrease of chlorophyll of the each rootstock was also one of the reasons for the decline of plant photosynthesis. Furthermore, we also used the chlorophyll fluorescence induction kinetic curve(OJIP) to reflect the changes of primary photochemical reaction information and electron transfer information of plant PSⅡ reaction center in a period of time. The characteristic sites of curves had changed when the different grape rootstocks were subjected to the saline-alkali stress. The O, J, I and P phases showed a downward trend in conclusion which flatted the OJIP curves. In the O-P standardized curve, the J phase showed an upward trend, and the I-P segment tended to be horizontal which indicated that saline-alkali stress would reduce the activity of PSⅡ reaction center and block the electron transfer in the reaction center, which subsequently affected the chlorophyll fluorescence intensity of the plant leaves. In addition, the most seriously affected variety was 5C among all varieties. The O point fluorescence intensity of 3309M, 420 and 5BB decreased which suggested that the reaction center in the photosynthetic process of these varieties was irreversibly inactivated. Being stressed by salt and alkali, the chlorophyll fluorescence parameters PSⅡ maximum photochemical efficiency(Fv/Fm), photochemical performance index(PIabs), light energy absorbed per unit area(ABS/CSm), light energy captured per unit area(TRo/CSm),quantum yield of electron transfer(ETo/CSm), the number of reaction centers per unit area(RC/CSm) decreased. However, the heat dissipation(DIo/CSm), Light energy absorbed by unit reaction center(ABS/RC), light energy captured by unit reaction center(TRo/RC) J(Vj) and I(Vi) point in the fluorescence induction curve increased. This results indicated that the ability of plant photosynthetic reaction center to inactivate, absorb light energy and capture light energy was reduced, a large amount of QAwas accumulated on the receptor side of PSⅡ reaction center, the transmission of electrons on the receptor side was blocked, the transmission ability of the electrons was reduced, the heat dissipation was high, and the utilization rate of light energy was weakened. To evaluate the relative ability of the different rootstocks on salt and alkali resistance, we formed a principal component analysis containing all these 18 indexes. It is found that in the first principal component, the Tr, Plabs, Fv/Fm, Vj, ABS/CSm, TRo/CSmand ETo/CSmwere the main indexes to evaluate the damage of rootstocks under salt-alkali stress. Among them, Tr was the indicators for regulating photosynthesis, Plabsand Fv/Fmwere the indicators for evaluating fluorescence ability, and ABS/CSm, TRo/CSm, Vj, ETo/CSmwere the important indicators for controlling light energy utilization. It seems to be possible that saline-alkali stress mainly affects plants by changing stomata and transpiration ability of leaves, as well as absorption, transmission, conversion and utilization ability of the leaves to the light energy.【Conclusion】Under saline-alkali stress, the growth of new plants of different grape rootstocks decreased, the synthesis of chlorophyll was blocked, and the photosynthetic fluorescence decreased. The order of the resistance degree(from strong to weak) to salt and alkali of the rootstocks was SO4, 1103P, 5BB, 420A, 3309M and 5C.