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

Elevated [CO₂] adversely affects spring growth in seedlings of the broad-leaf evergreen Eucalyptus pauciflora.

EGERTON, JOHN^*,1, BARKER, DAVID¹, BALL, MARILYN¹, ¹ CRC for Greenhouse Accounting, Research School of Biological Sciences, Australian National University., Canberra, ACT, Australia

ABSTRACT- Eucalyptus pauciflora was grown in open-topped chambers separated into east and west-facing populations by shade cloth. Leaves intercepted similar irradiance, but during either morning or afternoon. During spring, when soil resources are abundant, west-facing plants were expected to accrue greater benefit to growth, as warmer afternoon conditions would be more conducive to photosynthesis. During spring, an 11% greater relative growth rate (RGR) in west than east-facing plants was attributed to a 27% greater net assimilation rate (NAR) and a 12% lower leaf area ratio (LAR). Although allocation to roots was greater in west than east-facing plants, the lower LAR was due to thicker leaves. In contrast, elevated [CO₂] enhanced RGR of east-facing plants by 7%, consistent with 17% increase in NAR coupled with 9 % decrease in LAR. However, west-facing plants suffered greater frost damage under elevated [CO₂] and entered spring with 25% lower LAR. These plants were slow to initiate growth, resulting in 33% less biomass but recovery of LAR. Nevertheless, the small root system may have constrained access to soil resources as spring became warmer and drier, thereby limiting NAR. NAR was 75% lower under elevated than ambient [CO₂], accounting for the 75% lower RGR. Thus, asymmetry between growth of east and west facing plants may change under future CO₂ rich atmospheres, as greater vulnerability to frost causes west-facing plants to lose their spring growth advantage.

KEY WORDS: Eucalyptus, Frost, Elevated [CO₂], Relative Growth Rate