PARENT SESSION
Oral Session # 66: Ecological Studies at Biosphere II.
Presiding: ML Martinez Vazquez
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 104.

Diurnal leaf growth variations in Populus deltoides grown at different external CO₂ -concentrations.

Walter, Achim^*,1, Christ, Maja^{1, 2}, Barron-Gafford, Greg¹, Murthy, Ramesh¹, ¹ Biosphere 2 Center, Oracle, AZ, USA² Forschungszentrum Julich, Julich, Germany

ABSTRACT- Cottonwood trees (Populus deltoides Bartr.) were grown in three different CO₂-concentrations (40, 80 and 120 Pa) within the environmentally controlled Intensive Forestry Mesocosm at the Biosphere 2 Center, Oracle, AZ. Diurnal leaf growth characteristics of trees within three mesocosms were monitored both with a conventional and a digital image sequence processing method for several months. The novel imaging method was performed for the first time under relatively realistic environmental conditions, as opposed to a growth chamber. The results show that diurnal courses develop gradually throughout the vegetation period and that their amplitude depends on ambient CO₂-concentration. Decreased amplitudes were found in elevated CO₂. Phasing of the diurnal courses of different leaves was identical, irrespective of treatment and positions along the architecture of the plant. The distribution of growth within the plant, however, was affected by the CO₂ treatment. Results are discussed on the background of environmental constraints, the photosynthetic performance and the overall carbon balance of the different treatments.

Key words: Growth technology, CO₂, Biosphere 2, Leaf growth