PARENT SESSION
Oral Session #10: Elevated CO₂.
Presiding: D. Hileman
Monday, August 5. 8:00 AM to 11:30 AM. Grand Ballroom East, Radisson.

Effects of elevated [CO₂] on leaf physiology and phenology on over-wintering Eucalyptus.

BARKER, DAVID^*,1, EGERTON, JOHN¹, BALL, MARILYN¹, ¹ CRC for Greenhouse Accounting, Research School of Biological Sciences, Australian National University, Canberra, A.C.T., Australia

ABSTRACT- Interactive effects of high light and temperature stress under elevated [CO₂] were studied by comparing photosynthetic and growth parameters of seedlings of the broad-leaf evergreen Eucalyptus pauciflora grown in open-topped chambers separated into east- and west-facing populations by shade screens. Averaged over both orientations, with the first autumn frost leaf damage was 10 times higher in elevated vs. ambient [CO₂] chambers. However, irrespective of [CO₂], there was 2-fold more leaf damage to west- than east-facing leaves, a curious finding given previous results relating damage to morning low temperature and high light, and the assumed protection screens should have conferred on west-facing leaves. Greater leaf damage was correlated with lower PSII efficiency in west-facing leaves under elevated [CO₂]; however, over the course of the winter PSII efficiency was not lower in west-facing leaves. Average stomatal conductance was significantly lower for west- than east-facing leaves, and lower for elevated- vs. ambient-grown leaves. Yet, there was no significant difference in rates of leaf CO₂ assimilation. By the end of winter, breaking of leaf bud dormancy was significantly delayed and fewer buds were produced for west-facing plants under elevated [CO₂]. Thus, loss of photosynthetic tissue and delay in cold-acclimation during autumn led to the lowest spring growth rate and biomass accumulation in west-facing plants grown under elevated [CO₂]. Apparently, amplified stress effects under elevated [CO₂] in autumn adversely affect plant growth during spring.

KEY WORDS: elevated [CO₂], photosynthesis, cold-acclimation, Eucalyptus