Revista Chilena de Historia Natural 79 (1): 41-53, 2006
RESEARCH ARTICLE
Photosynthetic performance of Colobanthus quitensis (Kunth) Bartl.
(Caryophyllaceae) in a high-elevation site of the Andes of central Chile
Photosynthesis of Colobanthus quitensis and mesoclimatic conditions of air
temperature and light intensity during the growing season were investigated at 2,650 m in the central Chilean Andes. On three typical
days of the growing period (January, March and May), CO<sub>2</sub> 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 µmol CO<sub>2</sub> m<sup>-2</sup>s<sup>-1</sup>) during the morning and noon in days with high
photosynthetic active radiation (PAR, above 1,800 µmol photons m<sup>-2</sup>s<sup>-1</sup>). Pn increase in the afternoon (3.5- 4.8 µmol
CO<sub>2</sub> m<sup>-2</sup>s<sup>-1</sup>) when PAR decreased to ca. 1,400 µmol photons
m<sup>-2</sup>s<sup>-1</sup> and leaf temperature were ca. 20 ºC.
F<sub>v</sub>/F<sub>m</sub> in the diurnal periods was between 0.7-0.75 without evidence of photoinhibition.
Leaves at 15 and 22 ºC exhibited a slow decrease of F<sub>PSII</sub> with the increase in actinic light intensity, although the fraction of
reaction centers open (expressed by q<sub>P</sub>) remained higher at 22 ºC. NPQ was saturated at light intensities close
to 500 µmol photons m<sup>-2</sup>s<sup>-1</sup> in leaves at 22 ºC and at higher intensities at 15 ºC,
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.
Key words:
net photosynthesis,
chlorophyll fluorescence, NPQ, alpine climate, alpine plants, Andes
