| Summary: | Photosynthesis of Colobanthus quitensis and mesoclimatic conditions of air temperature and light intensity during the growing season were investigated at 2,650 in ill the central Chilean Andes. Oil three typical days of the growing period (January, March and May), CO2 exchange and chlorophyll fluorescence were measured. In addition, a series of fluorescence response curves with increasing light intensity at different temperatures were performed to estimate the propensity of Andean C. quitensis Populations to be photoinhibited. Net Photosynthesis (Pn) was low (ca. 2.0 mu mol CO2 m(-2)s(-1)) during the morning and noon in days with high photosynthetic active radiation (PAR. above 1,806 mu mol photons m(-2) s(-1)). pil increased in the afternoon (3.5-4.8 mu mol CO2 m(-2)s(-1)) when PAR decreased to ca. 1,400 mu mol photons m(-2)s(-1) and leaf temperature were ca. 20 degrees C. F-v/F-m in he diurnal periods was between 0.7-0.75 without evidence of photoinhibition. Leaves at 15 and 22 degrees C exhibited a slow decrease of Phi(PSII) with the increase in actinic light intensity, although the fraction of reaction centers open (expressed by q(p)) remained higher at 22 degrees C. NPQ was saturated at light intensities close to 500 mu mol photons m(-2)s(-1) in leaves at 22 degrees C and at higher intensities at 15 degrees C, suggesting that NPQ could be a mechanism of energy dissipation at high light intensity and high leaf temperature in the field. Our results indicated that C. quitensis is not photodamaged during the diurnal cycle and that the low Pn registered during some diurnal periods are likely to be related with photorespiration, which has been suggested as an efficient protective mechanism for photoinhibition in alpine plants. Our results are also compared with the photosynthetic performance of C. quitensis populations from the maritime Antarctic.
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