PHOTOSYNTHETIC ACTIVITY OF LEAVES OF PINUS-RADIATA AND NOTHOFAGUS-FUSCA AFTER 1 YEAR OF GROWTH AT ELEVATED CO2

Radiata pine (Pinus radiata D.Don) and red beech (Nothofagus fused (Ho ok.f.) Oerst.) were grown for over 1 year at elevated (ELEV, 64 Pa) an d ambient (AMB, 38 Pa) CO2 partial pressure in open-top chambers. Spri ngtime measurements of overwintering leaves showed that light- and CO2 -saturated photosynthetic rates (A,,) of pine leaves were similar for the two treatments (AMB: 6.7 +/- 1.08 mu mol m(-2) s(-1), mean +/- 1 s .e.; ELEV: 6.6 +/- 0.47) but, for beech leaves, A(max) was greater for AMB plants (8.8 +/- 0.90 mu mol m(-2) s(-1)) than for ELEV plants (6. 10 +/- 0.71). Summertime measurements of leaves grown that spring show ed that for pine, A(max) was similar in the two CO2 treatments (AMB 14 .9 mu mol m(-2) s(-1) +/- 0.80; ELEV: 13.5 +/- 1.9) while, for beech, A(max) was higher in AMB plants (21.0 +/- 1.1) than in ELEV plants (17 .2 +/- 1.9), although the difference was not statistically significant . These results indicate downregulation of photosynthetic capacity of beech but not pine. V-cmax did not differ between treatments within sp ecies, suggesting that there was no acclimation of rubisco activity. T riose phosphate utilisation limitation may have contributed to the dow nregulation of A(max) in beech. For pine, photosynthesis at treatment CO2 partial pressures was greater in ELEV plants in both spring and su mmer. For beech measured at treatment CO2 partial pressures, photosynt hesis was greater in ELEV plants in summer, but was similar between tr eatments in the springtime.