© 2005 Heron Publishing—Victoria, Canada
Seasonal changes in photosynthesis and photoprotection in a Quercus ilex subsp. ballota woodland located in its upper altitudinal extreme in the Iberian Peninsula
L. Corcuera (1), F. Morales (2), A. Abadía (2) and E. Gil-Pelegrín (1, 3)
1. Centro de Investigación y Tecnología Agroalimentaria de Aragón, Gobierno de Aragón, Apdo. 727, 50080 Zaragoza, Spain / 2. Department of Plant Nutrition, Aula Dei Experimental Station, CSIC, Apdo. 202, 50080 Zaragoza, Spain / 3. Corresponding author (egilp@aragob.es) / Received June 10, 2004; accepted October 30, 2004; published online March 1, 2005
Summary
Quercus ilex L. subsp. ballota (Desf.) Samp., a Mediterranean evergreen species growing in a continental Mediterranean climate, did not experience water
stress and showed greater sensitivity to winter stress than to summer stress over a 12-month period. Net CO2 assimilation rates and photosystem II (PSII) efficiency decreased markedly during the cold months and recovered completely
in spring. Lutein, neoxanthin and β-carotene to chlorophyll (Chl) molar ratios all showed the same trend throughout the year,
increasing from September to March. This increase was a result of increases in carotenoid concentrations, because Chl concentration
per unit leaf area remained stable, and was higher at the end than at the beginning of the first growing season. Lutein-epoxide
was a minor component of the total lutein pool. Thermal energy dissipation and non-photochemical quenching (NPQ) were associated
with the de-epoxidated forms of the xanthophyll cycle pigments in the warm months. Photosynthetic rates decreased slightly
at midday in summer. These changes were accompanied by decreases in maximum potential PSII efficiency (which recovered during
the night), actual and intrinsic PSII efficiencies, photochemical quenching and increases in NPQ. Overall, our data indicate
down-regulation of photosynthesis during the summer. The diurnal de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin
occurred throughout the year, except in January. Antioxidant enzymatic activity increased in the winter months, especially
during the coldest months, highlighting its key role in photoprotection against photo-oxidation. Structural and functional
modifications protected PSII from permanent damage and allowed 1-year-old leaves to photosynthesize at high rates when temperatures
increased in spring.
Keywords:
antioxidant enzymatic activity, chlorophyll fluorescence, photosynthetic pigments, summer stress, winter stress.
