Effect Of Chemical Agents Spraying On Alleviating Major Eco-environmental Stresses In Grape Growing Season

With the global warming,extreme weather events have been occurring frequently.High temperature and strong light can result in decrease of the photosynthetic efficiency and serious photoinhibition in grape leaves.The phenomenon of fruit sunburn and gasburn has become increasingly common,accompanied with the dramatic change of wind and temperature,which has caused damage to the grape production.In this study,several chemicals recommended for production were used to study the effects of different stressed climate on the daily changes of leaf photosynthentic parameters,leaf membrane protection systems,photosystem II?PSII?activity and fruit quality with eight-year-old�Vidal'grape as experimental material.The results are as follows:1.Under dry hot wind stress,with the increase of temperature and light intensity,the vapor pressure deficit?VPD?increased.The net photosynthetic rate?Pn?and the stomatal conductance?Gs?in the grape leaves gradually decreased.The Pn at 11:00 decreased by18.75%,compared with that at 9:00.The photosystem II?PSII?maximum photochemical efficiency?Fv/Fm?,density of reaction centers?RC/CSm?and a trapped exciton can move an electron into the electron transport chain beyond Q_A??Eo?decreased,meanwhile the relative fluorescence intensity of K point?Wk?increased.However,nonphotochemical quantum yield of PSI?[Y?NA?]?did not changed much.Non-photochemical quenching?NPQ?increased with the increase of light and temperature,but the increased level did not dissipated all the excessive light energy,which caused seriou PSII photoinhibiton.The spraying of several chemicals alleviated the PSII damage under dry hot wind stress,and increased the level of Fv/Fm,RC/CSm and?Eo,in which the abscisic acid?ABA?showed better effect.Compared with the control,the level of RC/CSm at 15:00 increased by74.5%,57.3%and 2.0%in the treatment of ABA,brassinolide?BR?,fulvic acid potassium?FA-K?,respectively.Meanwhile,the level of?Eo increased by 120%,17%and 25%,respectively.2.Under the combined stress of high temperature and high light,the photosynthetic parameters changed much in grape leaves.Pn and Gs decreased,meanwhile Ci increased,indicating that the cause of photosynthesis rate drop was non-stomatal limitation.With the high temperature and high light stress degree intensifying,the level of Fv/Fm further decreased and Wk increased,indicating that the combinded stress of high temperature and high light caused serious PSII photoinhibition in grape leaves.The spraying of several chemicals alleviated the inhibition of photosynthesis under the combined stress of high temperature and high light.Compared with the control,the level of Pn at 13:00 increased by 26.8%?22.4%?13.0%and 13.7%in the treatment of ABA,BR,FA-K and sodium bisulfite?NaHSO₃?,respectively.The level of Ci decreased by 18.2%,9.0%,9.5%and 10.0%,respectively.The analysis of chlorophyll fluorescence parameters showed that the spraying of several chemicals alleviated the damage to PSII under the combined stress of high temperature and high light,which increased the level of Fv/Fm?RC/Csm and?Eo,in which the treatment of BR showed better effects,followed by the treatment of ABA,FA-K and NaHSO₃.Compared with the control,the level of Fv/Fm,RC/CSm and?Eo in BR treatment increased by 10.9%,28.6%and 39.9%,respectively.3.The activities of SOD,POD and CAT in grape leaves increased first and then decreased under the combined stress of high temperature and high light with different response time and intensity.The treatment of BA showed more obvious effects.With the increase of temperature and light,the SOD activity increased rapidly and reached the highest value at 11:00,then remained at 13:00.The peak value was 64.9%higher than that of the control.At 13:00,the peak value of POD activity reached 180?g/g/min which was 69.8%higher than the control.The CAT activity reached the peak value at 13:00 which was 25.0%higher than the control,then slightly decreased.Treatment of ABA increased POD activity effectively,and the peak value was 160?g/min,which was 50.9%higher than that of the control.The peak value of CAT and SOD activities were 33.3%and 50.1%higher than that of the control,respectively,and there were no significant effects in the treatments of other chemicals.4.Under the combined conditions of high humidity?the relative air humidity remainedwithin 65%-80%from 9:00 to15:00 on the selected day?,high-temperature,high-light(the maximum light intensity reached 1775?mol�m^-2�s^-1 at 11:00,the highest temperature was37.9�C at 13:00)resulted in the decrease of Pn in grape leaves from 11:00,but showed the lowest value of 13.3?mol�m^-2�s^-1,the diurnal variation of Gs was consistent with Pn.The Ci showed a increased trend and reached the highest at 13:00.Compared with the control,different chemical treatments did not show significant alleviated effects role,indicating that high humidity might be helpful to the alleviation of high temperature and light interaction stress.5.The spraying of different chemicals increased the soluble solids content in the mature grapes?7.8%¹4.7%?significantly,compared with the control.The treatment of FA-K shower better effects,but there was no significant difference in different treatments.The spraying of chemicals reduced the titratable acid contents and increased the tannin contents,in which the treatment of BR showed better effects,which increased by 54%,compared with the control,followed by ABA and FA-K,which increased by 28.3%and 26.2%.The total phenols content in BR treaments was 15.8%higher than that of the control.There were no significant differences in other treatments.