The Researches Of Chlorophy? Fluorescence Characteristics Of Zea Mays And Cotton At Different Growth Stages And High Temperature

Maize(Zea mays L.)isn't only an important food and feed crops,but also China's first major crop.According to statistics,maize is one of the three major cereals,its planting area after rice,wheat,but the total output ranks first in the three grains.It's the crop which has the world's largest acreage expansion and the largest increase in yield per unit area of field in the past hundred years.The Cotton(Gossypium hirsutum L.)isn't only the world's most important natural fiber crops,but also China's important economic crops.China isn't only currently the world's largest cotton producer,consumer and importer,but also the largest exporter of cotton textiles.With the global warming,the impact of high temperature on the production of maize and cotton is increasing,and the high temperature will adversely affect the photosynthesis process^ photosynthetic product accumulation and yield formation of maize and cotton.It is predicted that the temperature will increase at least 1.1-2.1 ? inthe end of this century.unpredictable periodic high temperature strength and frequency will continue to increase in the future.In future the maximum temperature in most parts of China will be significantly increased,extreme weather and high temperature events showed an increasing trend.To cultivate high temperature resistant cotton and maize varieties is of great significance in tackling global warming.However,high temperature resistance and high photosynthetic efficiency germplasm resources evaluation technology is still not perfect.The chlorophyll fluorescence parameters mainly reflect the photosynthetic system(PS II)primary photochemical reaction and photosynthetic mechanism,the state change of chlorophyll fluorescence parameters with gas exchange indicators to better reflect the "intrinsic"characteristics of photosynthetic system.In this study,maize and upland cotton varieties(lines)with different heat tolerance were selected to measure the leaf chlorophyll fluorescence at different growth stages.The effects of field temperature and in vitro high temperature treatments on photosynthetic performance of maize and cotton leaves were studied.The changes of fluorescence parameters of maize and cotton leaves were studied before and after high temperature treatment,and a good fluorescence parameter was selected in all 47 fluorescence parameters for rapid identification the high temperature resistant varieties with high photosynthetic efficiency in maize and cotton.The results of this study are as follows:1.The results showed that there were 24 parameters showing an upward trend in maize leaves after high temperature treatment,namely,Area,Fo,F1,F2,F3,Fo/Fm,dV/dto,dVG/dto,PSIo,PHI(Eo),PHI(D),Sm,N,Sm/T(fmax),Kn,ABS/RC,TRo/RC,ETo/RC,DIo/RC,ABS/CSo,ETo/CSo,Dlo/CSo,DIo/CSm,PSIo/(1-PSIo).The parameters of the descending trend were 21,which were:Fm,F4,F5?Fv/Fo,Vj,Vi,PHI(Po),Sum K,Kp,RC/Cso,RC/CSm,ABS/CSm,TRo/CSm,ETo/CSm,SFI(abs),1ORC/ABS,PHIo/(1-PHIo),PI(abs),PI(cso),PI(csm),D.F.There were two parameters with unknown trends:Tf(max),TRo/CSo.After treatment at 35 0C at Seedling Stage,there were 13 parameters significantly changed at 5%(P<0.05),which were:Area,Fo/Fm,Fv/Fo,PHI(Po),PHI(Eo),PHI(Do),Sm,N,ABS/RC,TRo/RC,DIo/RC,10RC/ABS,PHIo/(1-PHIo).There are 11 parameters significantly changed at 1%(P<0.01)5 which are:F4,F5,Vj,Vi,PSIo,Sm/T(fixax),ETo/RC,RC/Cso,ETo/CSo,RC/CSm,PSIo/(1-PSIo).Among them,there were three parameters,F3,F4,ETo/CSm,which were significant at 5%after treatment at 40°Cin Flowering period..There were 37 parameters significantly changed at 1%,which were:Area,Fo,Fm,Fl1 F2,F5?Fo/Fm,Fv/Fo,dV/dto,dVG/dto,Vi,PHI(Po/RC,TRo/RC,ETo/RC,DIo/RC,RC/CSo,ABS/CSo,ABS,DIo/CSo,RC/CSm,ABS/CSm,TRo/CSm,DIo/CSm,SFI(abs),10RC/ABS,PHIo/(1-PHIo),PI(abs),PI(cso),D.F.It can be seen that the 40 °C high temperature treatment more than 35 0C reflected the change in the parameters.2.Through measuring all the fluorescence parameters in different growth stages of maize,it can be seen that the seedling(May 25)showed better performance in the 10 parameters of the 47 chlorophyll fluorescence parameters;the jointing stage(June 7)performed better in the 21 parameters;the trumpet stage(June 21)performed better in the 38 parameters;the same as trumpet stage later stage and the flare opening stage;the flare opening stage(June 30)showed better performance in 40 parameters;the silking stage(July 22)showed better performance in 11 parameters;in the silking later stage(July 22)showed better performance in 16 parameters;the mature period(August 1)showed better performance in 18 parameters.Thus,the entire trumpet period(that is the small trumpet period to the flare opening later stage)in most of the parameters had good performance.The trumpet period can be determined as the best measurement period of maize chlorophyll fluorescence parameters.3.Field high temperature can make the following 22 chlorophyll fluorescence parameters of cotton leaves increased:Area?Fv/Fo?PHI(Po),PSIo,PHI(Eo),Sm,Sm/T(fmax),Sum K,Kn,Kp,ETo/CSo,RC/CSm,TRo/CSm,ETo/CSm,SFI(abs),10RC/ABS,PHIo/(1-PHIo),PSIo/(1-PSIo),PI(abs)Cso),PI(csm),DF..The following 19 chlorophyll fluorescence parameters of cotton leaves showed a downward trend after field high temperature treament:Fm,F1,F2,F3,F4,F5,Fo/Fm,dV/dto,dVG/dto,Vj,PHI(Do),ABS/RC TRo/RC,DIo/RC,RC/CSo,ABS/CSo,TRo/CSo,DIo/CSo,DIo/CSm.The chlorophyll fluorescence parameters that influenced by the field temperature on the cotton leaves was not obvious are the following six parameters:Tf(max),Fo,Vi,N,ETo/RC,ABS/CSm.In this study,the technical indexes of thermostability and high efficiency varieties of maize and cotton were established.The trends of chlorophyll fluorescence parameters of maize and cotton leaves under high temperature stress were clarified,and the numerical level and trend of change of chlorophyll fluorescence parameters were also clarified in different growth stages of maize and cotton.This study has an important significance to improve the high temperature resistance and high photosynthetic efficiency germplasm resources evaluation technology,and to establish the parameters of chlorophyll fluorescence method for use after high temperature stress and daily measurement on maize and cotton.In this study,the chlorophyll fluorescence parameters PI(abs),which were representative and able to reflect the high temperature tolerance of photosynthetic system in maize and cotton varieties,were selected from all 47 indicators.The PIcould be used as an auxiliary index for selecting thermostability and high efficiency maize and cotton varieties.