Kinetics of leaf temperature fluctuation affect isoprene emission from redoak (Quercus rubra) leaves

Because the rate of isoprene (2-methyl-1,3-butadiene) emission from plants is highly temperature-dependent, we investigated natural fluctuations in le af temperature and effects of rapid temperature change on isoprene emission of red oak (Quercus rubra L.) leaves at the top of the canopy at Harvard F orest, Throughout the day, leaves often reached temperatures as much as 15 degrees C above air temperature. The highest temperatures were reached for only a few seconds at a time. We compared isoprene emission rates measured when leaf temperature was changed rapidly with those measured when temperat ure was changed slowly. In all cases, isoprene emission rate increased with increasing leaf temperature up to about 32 degrees C and then decreased wi th higher temperatures, The temperature at which isoprene emission rates be gan to decrease depended on how quickly measurements were made. Isoprene em ission rates peaked at 32.5 degrees C when measured hourly, whereas rates p eaked at 39 degrees C when measurements were made every four minutes. This behavior reflected the rapid increase in isoprene emission rate that occurr ed immediately after an increase in leaf temperature, and the subsequent de crease in isoprene emission rate when leaf temperature was held steady for longer than 20 minutes. We concluded that the observed temperature response of isoprene emission rate is a function of measurement protocol. Omitting this parameter from isoprene emission models will not affect simulated isop rene emission rates at mild temperatures, but can increase isoprene emissio n rates at high temperatures.