PARENT SESSION
Oral Session #4: Plant Ecology: Gas Exchange. Presiding: J. Pereira.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas P&Q.
Elevated CO2 growth conditions suppress isoprene emissions from cottonwood trees (Populus deltoides) grown in an enclosed ecosystem.
Potosnak, Mark1, Griffin, Kevin1, Murthy, Ramesh2, van Haren, Joost2, Monson, Russel3, 1 2 3
ABSTRACT- Cottonwood tree hybrid clones were grown at the Biosphere 2 Center in Oracle, AZ during the 2000 growing season. One section of the facility was divided into 3 bays east to west with approximately 30 trees per bay and CO2 partial pressures of 38, 71, and 107 Pa respectively. The bays acted as large flow through chambers (~600 m2 surface area, ~1100 m3 volume) with push-pull fans continually supplying outside air and with CO2 injected to maintain the concentration set points. Continuous measurements of isoprene concentrations in the airspace of each bay combined with fan flow rates and leak rates determined by SF6 injection were combined to calculate whole system rates of isoprene production. These measurements were compared to modeled emission estimates from Dennis Baldocchi's CANVEG model driven by environmental data and monthly leaf level measurements. Elevated atmospheric CO2 partial pressures suppressed basal rates of isoprene emission throughout the growing season and, except for several periods of drought stress, the 38 Pa bay had higher rates of emission (both whole system and leaf level) than the 71 and 107 Pa bays. During the two induced drought periods in July and November, basal rates of isoprene emission increased in the 71 and 107 Pa bays compared to the 38 Pa bay. These increases were matched by decreases in intercellular CO2 partial pressures related to drought induced decreases in stomatal conductance.
KEY WORDS: isoprene, carbon dioxide, Populus deltoides, enclosed ecosystems