Effect of elevated CO2on the utilization of light energy inNothofagus fuscaandPinus radiata

Abstract

Red beech (Nothofagus fusca (Hook. F.) Oerst.; Fagaceae) and radiata pine (Pinus radiata D. Don; Pinaceae) were grown for 16 months in large open-top chambers at ambient (37 Pa) and elevated (66 Pa) atmospheric partial pressure of CO 2 , and in control plots (no chamber). Summer-time measurements showed that photosynthetic capacity was similar at elevated CO 2 (light and CO 2 -saturated value of 17.2 μmol m -2 s -1 for beech, 13.5 μmol m -2 s -1 for pine), plants grown at ambient CO 2 (beech 21.0 pmol m -2 s -1 , pine 14.9 μmol m -2 s -1 ) or control plants grown without chambers (beech 23.2 μmol m -2 s -1 , pine 12.9 μmol m -2 s -1 ). However, the higher CO 2 partial pressure had a direct effect on photosynthetic rate, such that under their respective growth conditions, photosynthesis for the elevated CO 2 treatment (measured at 70 Pa CO 2 partial pressure: beech 14.1 μmol m -2 s -1 pine 10.3) was greater than in ambient (measured at 35 Pa CO 2 : beech 9.7 μmol m -2 s -1 , pine 7.0 μmol m -2 s -1 ) or control plants (beech 10.8 μmol m -2 s -1 , pine 7.2 μmol m -2 s -1 ). Measurements of chlorophyll fluorescence revealed no evidence of photodamage in any treatment for either species. The quantity of the photoprotective xantho-phyll cycle pigments and their degree of de-epoxidation at midday did not differ among treatments for either species. The photochemical efficiency of photosystem II (yield) was lower in control plants than in chamber-grown plants, and was higher in chamber plants at ambient than at elevated CO 2 . These results suggest that at lower (ambient) CO 2 partial pressure, beech plants may have dissipated excess energy by a mechanism that does not involve the xanthophyll cycle pigments.