Diurnal variation of gas exchange,chlorophyll fluorescence and xanthophylls cycle components in leaves of maize cultivars released in different years
【摘要】：正 Diurnal variation of gas exchange, chlorophyll fluorescence and xanthophylls cycle components in leaves of three maize (Zea mays L.) cultivars (Baimaya, Zhongdan2 and Nongda108) released in different years were compared. The aim of the study was try to find out their different response patterns in gas exchange and PS2 efficiency to changing photosynthetic photon flux density (PPFD). On cloudless days with solar radiation peaking at noon, the modern cultivars always had higher net photosynthetic rate (PN) than that of the old ones during the day especially at noon. At noon, all the three cultivars decreased their PS2 primarily chemical efficiency (Fv/Fm) and actual quantum yield of PS2(ΦPS2), with the modern ones having always the higher values. Modem cultivars also had high photochemical quenching of chlorophyll (qp) and low non-photochemical quenching (NPQ). The inter-cultivar differences in PN may be owing to their different photochemical efficiency. A midday depression in photosynthetic rate occurred in all cultivars, although it was not so typical as that of C3 plants. However, the depression was more obvious in the old cultivars particularly when they entered the senescent stage. Depression in PN might not be caused by stomatal closure, because intercellular CO2 concentration (Ci) did not increased with stomatal conductance (gs). It may be caused by serious photoinhibition of the senescent leaves at noon. The xanthophylls pool of the modern cultivar had higher ability in dissipating excess energy, indicating much higher ability in resisting photoinhibition.