Effect of elevated CO2 on the utilization of light energy in Nothofagus fusca and Pinus 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 CO2, and in control plots (no chamber). Summer-time measurements showed that photosynthetic capacity was similar at elevated CO2 (light and CO2-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 CO2 (beech 21.0 μmol m-1 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 CO2 partial pressure had a direct effect on photosynthetic rate, such that under their respective growth conditions, photosynthesis for the elevated CO2 treatment (measured at 70 Pa CO2 partial pressure: beech 14.1 μmol m-2 s-1 pine 10.3) was greater than in ambient (measured at 35 Pa CO2: 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 xanthophyll 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 CO2. These results suggest that at lower (ambient) CO2 partial pressure, beech plants may have dissipated excess energy by a mechanism that does not involve the xanthophyll cycle pigments.