Diurnal patterns of net photosynthetic rate, stomatal conductance, and chlorophyll fluorescence in leaves of field-grown mungbean (Phaseolus radiatus) and millet (Setaria italica)

Abstract

The diurnal variations of net photosynthetic rate (Pn), quantum yield of photochemical quenching (YP), and non-photochemical quenching (YN) of photosystem II (PSII), as well as stomatal status were studied in leaves of field-grown mungbean (Phaseolus radiatus, C3 crop) and millet (Setaria italica, C4 crop) in arid and semi-arid regions of China. Although patterns of Pn in both crops were one-peak curves, the time that Pn peaks occurred was 0600 h for mungbean and 1000 h for millet. YP was always higher, whereas YN was lower in mungbean leaves than in millet. By analysing the pool size of the primary electron acceptor of PSII (QA), it was indicated that millet leaves had a higher capacity to control or regulate the reduction state of QA, thus dissipating excessive energy under intense irradiance and high ambient temperature, and therefore advantageous to leaf photosynthesis in millet. Midday depression of stomatal conductance occurred in both crops, but played different roles on leaf photosynthesis in mungbean and millet. Additionally, stomatal regulation operated for much longer in millet leaves than in mungbean. In general, the present studies indicated that regulation of the QA reduction state and operation of stomata were two physiological factors contributing to millet being more adaptive than mungbean for cultivation in arid and semi-arid regions. © 2004 Taylor & Francis Group, LLC.