PSII photochemical efficiency in flag leaf of wheat varieties and its adaptation to strong sunlight intensity on farmland of Xiangride in Qinghai Province,Northwest China

Taking four wheat varieties developed by Northwest Institute of Plateau Biology,Chinese Academy of Sciences,as test materials,with the measurement of content of photosynthetic pigments,leaf area,fresh and dry mass of flag leaf,the PSⅡ photochemistry efficiency of abaxial and adaxial surface of flag leaf and its adaptation to strong solar radiation during the period of heading stage in Xiangride region were investigated with the pulse-modulated in-vivo chlorophyll fluorescence technique. The results indicated that flag leaf angle mainly grew in horizontal state in Gaoyuan 314,Gaoyuan 363 and Gaoyuan 584,and mainly in vertical state in Gaoyuan 913 because of its smaller leaf area and larger width. Photosynthetic pigments were different among the 4 varieties,and positively correlated with intrinsic PSⅡ photochemistry efficiencies( Fv/Fm). In clear days,especially at noon,the photosynthetic photoinhibition was more serious in abaxial surface of flag leaf due to directly facing the solar radiation,but it could recover after reduction of sunlight intensity in the afternoon,which meant that no inactive damage happened in PSⅡ reaction centers. There were significant differences of PSⅡ actual and maximum photochemical efficiencies at the actinic light intensity( ΦPSⅡand Fv' /Fm') between abaxial and adaxial surface,and their relative variation trends were on the contrary. The photochemical and non-photochemical quenching coefficients( qPand NPQ)had a similar tendency in both abaxial and adaxial surfaces. Although ΦPSⅡand qPwere lower in adaxial surface of flag leaf,the Fv' /Fm' was significantly higher,which indicated that the potential PSⅡ capture efficiency of excited energy was higher. The results demonstrated that process of photochemical and non-photochemical quenching could effectively dissipate excited energy caused by strong solar radiation,and there were higher adaptation capacities in wheat varieties natively cultivated in Qinghai-Tibetan Plateau area.