| Three dendrobia named Dendrobium primulinum, D. nobile, D.chrysotoxum were employed in the trials. Carbon assimilation, electron transport across the two photosystems were explored; the fluctuation of chlorophyll fluorescence related to PSII and P700 signal pertinent to PSI were investigated synchronously; the diurnal changes of malic acid contents in fresh leaves was measured; the diurnal changes of the activity of phosphoenolpyruvate carboxylase (PEPC) was inspected; stomata morphology and stomata movement were observed; moreover, the experiment design was initiated to realize synchronous study on the linkage between three physiological processes including carbon assimilation, electron transport and stomata movement.The results demonstrated that D.primulinum is a CAM (Crassulacean acid metabolism) species. Under normal conditions and in moderate arid environment, D.nobile and D.chrysotoxum performed C3 photosynthesis. However, serious drought could induce them switching into CAM pathway, furthermore, the carbon assimilation could operate unremittingly round the clock in D.chrysotoxum, and it always kept net absorb of carbon dioxide day and night.In green house during winter, the requirement for light condition was different significantly from one to another among the three dendrobia. D.primulinum and D.chrysotoxum could be adapt to the highlight as intense as 1000μmolphotonm-2s-1, while the light saturation point was 300μmolphotonm-2s-1. Generally, the photosynthetic rate was low in dendrobia. Among the three dendrobia, the maximum photosynthetic rate was 3.92μmolCO2m-2s-1in D.chrysotoxum during winter. Diurnal change of photosynthesis in D.primulinum exhibited typical feature of CAM with nocturnal carbon assimilation.In growth season, the light saturation point of D.primulinum declined to 300μmolphotonm-2s-1, and the maximum photosynthetic rate increased to 3.826μmolCO2m-2s-1. The diurnal change of photosynthesis was composed by four distinct phases. The light saturation point of D.chrysotoxum lowered to 800μmolphotonm-2s-1, and maximum photosynthetic rate rose to 5.912μmolCO2m-2s-1, while the diurnal change of photosynthesis showed single summit at noon.D.nobile preferred to shade environment, whose diurnal change of photosynthesis showed double summits, and there was photo inhibit at noon when illumination was intense.Activity of PEPC of D.primulinum from dark leaves was strong, whilst it was relatively weak at noon when sun light was bright. The diurnal change of activity of PEPC in D.nobile was resembled to D.primulinum. The activity of PEPC in D.chrysotoxum was very weak, and the magnitude of diurnal change was small; anyway, its activity from dark leaves was stronger than one from illuminated leaves.The maximal photochemical efficiency of PSII in D.primulinum during winter was lower than 0.8, and the photosynthetic apparatus was in abnormal state that there was chlorophyll deficiency, which indicated that D.primulinum fell into dormancy. The maximal photochemical efficiency in D.nobile was 0.828, but its actual photochemical efficiency and photochemical quenching coefficient were very small, which showed that its photosynthesis was sluggish and was dormant to some certain during winter. D.chrysotoxum could perfectly acclimatize itself to the greenhouse environment in winter, its maximal photochemical efficiency was higher even as high as 0.8 when encountered to the chilling stress. The ratio for photochemistry from the energy absorbed by antenna pigment in D.chrysotoxum was high, and there were more open centers of PSII, which was conducive to electron transport so as to rapidly produce assimilatory power. Hence, the photosynthesis processes were vigorous in D.chrysotoxum during winter.After 2 hours of darkness treatment, the maximal fluorescence was lower than one of D.nobile which was in the same level based on the photosynthetic rate as D.primulinum, and the Fm was also lower than the value of maximal fluorescence of D.primulinum after 12 hours of darkness treatment. Therefore, there was electron transport in the D.primulinum treated in darkness for 2 hours, which probably related to chlororepiration.The effect of illumination period on photochemical reaction after darkness adaptation was significant. Longer than 4 hours of actinic light illumination was beneficial to operating efficiently of photosynthesis apparatus for C3 species including D.nobile and D. chrysotoxum. As to D.primulinum, 2 hours of illumination after darkness adaptation resulted in the maximal photosynthetic rate, and there was close relationship between photochemical reaction and carbon dioxide supply.Malic acid contents showed orderly diurnal fluctuation in the leaf of D.primulinum, and its rhythm demonstrated the characteristics of four phases exclusive to CAM species.The stomata of D.primulinum were nearly close when exposed to light intenser than actinic light, but its electron transport operated smoothly. It was found that there was unevenly stomata close in D.nobile and D.chrysotoxum. Stomata configuration were similar among the three dendrobia, their stomata apparatus types were anomocytic, without subsidiary cells, and there was a cuticle stomata ledge outside of guard cells.For the first time, chlorophyll fluorescence kinetics and P700 signal were simultaneously monitored and served as probe to study the electron transport across two photosystems in ornamental plants. For the first time, micro-observation was actualized on fresh leaf free from special treatment which disturbed the stomata movement, snapshooting the actual stomata uneven close. The blueprint tailored for synchronously exploring carbon assimilation, electron transport and stomata movement was initiated, and the primary experiment conducted lately foretold the bright future.
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