© 1996 Heron Publishing—Victoria, Canada
Photosynthetic and stomatal responses to high temperature and light in two oaks at the western limit of their range
Erik Hamerlynck (1, 2) and Alan K. Knapp (1)
1. Division of Biology, Kansas State University, Ackert Hall, Manhattan, KS 66506-4901, USA / 2. Department of Biological Sciences, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454004, Las Vegas, NV 89154-4004,
USA / Received May 25, 1995
Summary
Bur oak (Quercus macrocarpa Michx.) and chinquapin oak (Q. muehlenbergii Engl.) leaves were exposed to high temperatures at various photosynthetic photon flux densities under laboratory conditions
to determine if species-specific responses to these factors were consistent with the distribution of these oaks in gallery
forests in the tallgrass prairies of northeastern Kansas, USA. Measurements of the ratio of chlorophyll fluorescence decrease,
Rfd, indicated that chinquapin oak maintained greater photosynthetic capacity than bur oak across all tested combinations of
irradiance (100, 400, 700 and 1000 µmol m–2 s–1) and temperature (40, 42, 44, 46 and 48 °C). In both oak species, manipulation of leaf temperature to about 47 °C for 45
min in the field led to a 45% decrease in carbon assimilation up to one week after the heat treatment, and to sharp reductions
in stomatal conductance. Photosynthetic recovery patterns indicated that bur oak took longer to recover from heat stress than
chinquapin oak, suggesting that heat stress may be important in determining distribution patterns of these oak species. Based
on a comparison of the results with data from other forest species, we conclude that the photosynthetic temperature tolerances
of bur oak and chinquapin oaks facilitate their dominance at the western limit of the eastern deciduous forest.
Keywords:
chlorophyll fluorescence, heat stress, Quercus macrocarpa, Quercus muehlenbergii.
