Ammopiptanthus mongolicus (Maxim.) Cheng f. is one of the evergreen shrubs in the desert region of China. In midday its leaves bear photon flux density over 1 500 μmol·m -2 ·s -1 at natural habit...Ammopiptanthus mongolicus (Maxim.) Cheng f. is one of the evergreen shrubs in the desert region of China. In midday its leaves bear photon flux density over 1 500 μmol·m -2 ·s -1 at natural habitat. They show the obvious phenomenon of photoinhibition. For the study of the effects of drought stress on the major protective mechanism against strong light in A. mongolicus leaves, the diurnal variations of photosynthetic rate and chlorophyll fluorescence parameters were investigated under natural conditions with portable photosynthetic measurement system (CIRAS_1) and portable fluorometer (MFMS_2). The experimental results showed that, under normal and drought stress conditions,the net photosynthetic rate ( Pn ), the primary maximum photochemical efficiency of PSⅡ ( Fv/Fm ) and the quantum efficiency of noncyclic electron transport of PSⅡ ( Φ PSⅡ ) decreased obviously at noon (Figs.2,3A,4B). In comparison with plants under normal condition, under drought stress minimal chlorophyll fluorescence ( Fo ) decreased at first and then increased (Fig.3A), non_photochemical quenching ( NPQ ) quickly increased and sustained at a higher level (Fig.4B). This indicated that the major photoprotective mechanism of A. mongolicus leaves was the xanthophyll cycle_dependent thermal energy dissipation under normal condition, while under drought stress, the major photoprotective mechanism was both the xanthophyll cycle_dependent thermal energy dissipation and the reversible inactivation of PSⅡ reaction center.展开更多
文摘Ammopiptanthus mongolicus (Maxim.) Cheng f. is one of the evergreen shrubs in the desert region of China. In midday its leaves bear photon flux density over 1 500 μmol·m -2 ·s -1 at natural habitat. They show the obvious phenomenon of photoinhibition. For the study of the effects of drought stress on the major protective mechanism against strong light in A. mongolicus leaves, the diurnal variations of photosynthetic rate and chlorophyll fluorescence parameters were investigated under natural conditions with portable photosynthetic measurement system (CIRAS_1) and portable fluorometer (MFMS_2). The experimental results showed that, under normal and drought stress conditions,the net photosynthetic rate ( Pn ), the primary maximum photochemical efficiency of PSⅡ ( Fv/Fm ) and the quantum efficiency of noncyclic electron transport of PSⅡ ( Φ PSⅡ ) decreased obviously at noon (Figs.2,3A,4B). In comparison with plants under normal condition, under drought stress minimal chlorophyll fluorescence ( Fo ) decreased at first and then increased (Fig.3A), non_photochemical quenching ( NPQ ) quickly increased and sustained at a higher level (Fig.4B). This indicated that the major photoprotective mechanism of A. mongolicus leaves was the xanthophyll cycle_dependent thermal energy dissipation under normal condition, while under drought stress, the major photoprotective mechanism was both the xanthophyll cycle_dependent thermal energy dissipation and the reversible inactivation of PSⅡ reaction center.
