Isoprene (2-methyl-1,3-butadiene) emission from plants is highly temperature dependent. The influence of long-term variations in growth temperature on isoprene emission rates from bur oak (Quercus macrocarpa) leaves was investigated under controlled environmental conditions. Trees were installed in a growth chamber and exposed to a series of daytime temperatures that were varied after a period of 3--6 weeks. Emission capacity (measured at leaf temperature of 25 ¿C and photosynthetic photon flux density of 900 &mgr;mol m-2 s-1) doubled when growth temperature was increased from 25 to 30 ¿C. Ten days after the growth temperature was decreased to 20 ¿C, isoprene emission capacity fell to 25 to 50% of its peak value. When growth temperature was returned to 30 ¿C, emission capacity doubled within 5 hours and continued to increase over several days. The observed behavior can be described by modifying existing algorithms. ¿ 2001 American Geophysical Union