PARENT SESSION
Oral Session #54: Vegetation: Controls on NPP, Global Climate Change. Presiding: W. Oechel.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.

Interactive effects of nitrogen, microclimate and elevated CO₂ on tree seedling growth under field conditions.

EGERTON, JOHN¹, BALL, MARILYN¹, ¹

ABSTRACT- Interactive effects of soil nitrogen and elevated atmospheric CO₂ on growth of seedling snow gum (Eucalyptus pauciflora) were studied under field conditions in open-topped chambers flushed with either ambient air or air enriched to 700 ppm CO₂. In autumn, seedlings grown under elevated CO₂ suffered greater injury during early freezing events. Median losses in canopy areas were 23.9 and 1.3 % under elevated and ambient CO₂, respectively, with losses under elevated CO₂ declining from 34.1 to 13.4 % with decrease in nitrogen. In early spring, when temperatures were favourable and soil water content was high, plants in elevated CO₂ showed more rapid growth than those in ambient CO₂, with plants in the high nitrogen treatment taking most advantage of the high CO₂. However, seedlings under elevated CO₂ began to lose their growth advantage during an episode of high temperatures and drought in early summer, with adverse effects on photosynthesis, growth and survival exacerbated by increase in soil nitrogen. By the end of a year, survival was lower and growth of surviving seedlings was greater under elevated CO₂, but growth was much less than it would have been if the seedlings had not been more sensitive to both low and high temperature stress.

KEY WORDS: microclimate, elevated CO₂, nitrogen, Eucalyptus pauciflora