© 1996 Heron Publishing—Victoria, Canada
Field measurements of isoprene emission from trees in response to temperature and light
Thomas D. Sharkey (1), Eric L. Singsaas (1), Peter J. Vanderveer (1) and Chris Geron (2)
1. Department of Botany, 430 Lincoln Drive, University of Wisconsin, Madison, WI 53706, USA / 2. National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA / Received July 10, 1995
Summary
The atmospheric hydrocarbon budget is important for predicting ozone episodes and the effects of pollution mitigation strategies.
Isoprene emission from plants is an important part of the atmospheric hydrocarbon budget. We measured isoprene emission capacity
at the bottom, middle, and top of the canopies of a white oak (Quercus alba L.) tree and a red oak (Quercus rubra L.) tree growing adjacent to a tower in the Duke University Forest. Leaves at the top of the white oak tree canopy had a
three- to fivefold greater capacity for emitting isoprene than leaves at the bottom of the tree canopy. Isoprene emission
rate increased with increasing temperature up to about 42 °C. We conclude that leaves at the top of the white oak tree canopy
had higher isoprene emission rates because they were exposed to more sunlight, reduced water availability, and higher temperature
than leaves at the bottom of the canopy. Between 35 and 40 °C, white oak photosynthesis and stomatal conductance declined,
whereas red oak (Quercus rubra) photosynthesis and stomatal conductance increased over this range. Red oak had lower rates of isoprene emission than white
oak, perhaps reflecting the higher stomatal conductance that would keep leaves cool. The concentration of isoprene inside
the leaf was estimated with a simplified form of the equation used to estimate CO2 inside leaves.
Keywords:
isoprene, Quercus alba, Quercus rubra, red oak, temperature, white oak.
