Study on the Photosynthetic Characteristics of Citrus aurantium in Summer
[Objective]To study the photosynthetic characteristics of Citrus aurantium in summer.[Method]By using Li-6400 portable photo-synthesis system,the net photosynthetic rate(Pn)of leaves in different positions,diurnal variation of photosynthesis,light response curve and CO2 response curve of Citrus aurantium were measured.[Result]There were certain differences in Pn of leaves in different directions and parts.The diurnal variation of Pnof Citrus aurantium in summer showed a double-peak curve with a"nap"phenomenon,and the photosynthetic peaks appeared at 10:00 and 14:30,respectively.The diurnal variation of stomatal conductance was similar to that of Pn.From the light re-sponse curve,it could be seen that Citrus aurantium had a high saturation point and a light intensity of 0-2 000 μmol/(m2·s),the Pn contin-ued to increase,reaching a maximum of 13.44 μmol/(m2·s),with a light compensation point of 28.33 μmol/(m2·s),the apparent quantum efficiency was 0.036.From CO2 response curve,the CO2 saturation point and CO2 compensation point were about 1 500 μmol/mol and 60.65 μmol/mol,respectively,and the carboxylation efficiency was 0.079.The results of correlation and regression analysis showed that in sum-mer Pnof Citrus aurantium was closely associated with physiological and ecological factors,such as stomatal conductance,relative humidity,in-tercelluar CO2 concentration,transpiration rate,vapor pressure deficienc.[Conclusion]Citrus aurantium was a heliophile C3 plant and it had a strong ability to adapt and utilize low light and strong assimilation ability to CO2.And under the high temperature and low air relative humidity in summer,the photosynthesis of Citrus aurantium was affected by various physiological and ecological factors.In this period,the photosynthet-ic active radiation was not the key factor affecting Pn,and the air relative humidity was significantly positively correlated with Pn.Therefore,environmental selection or cultivation measures to increase the air relative humidity could mitigate the midday depression of photosynthesis in summer and improved the photosynthetic efficiency of Citrus aurantium.
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