© 2000 Heron Publishing—Victoria, Canada
Acclimation of photosynthesis and respiration to simulated climatic warming in northern and southern populations of Acer saccharum: laboratory and field evidence
Carla A. Gunderson (1), Richard J. Norby (1) and Stan D. Wullschleger (1)
1. Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008 MS-6422, Oak Ridge, TN 37831-6422, USA / Received November 18, 1998
Summary
Physiological acclimation and genotypic adaptation to prevailing temperatures may influence forest responses to future climatic
warming. We examined photosynthetic and respiratory responses of sugar maple (Acer saccharum Marsh.) from two portions of the species’ range for evidence of both phenomena in a laboratory study with seedlings. A field
study was also conducted to assess the impacts of temperature acclimation on saplings subjected to an imposed temperature
manipulation (4 °C above ambient temperature). The two seedling populations exhibited more evidence of physiological acclimation
to warming than of ecotypic adaptation, although respiration was less sensitive to short-term warming in the southern population
than in the northern population. In both seedling populations, thermal compensation increased photosynthesis by 14% and decreased
respiration by 10% in the warm-acclimated groups. Saplings growing in open-top field chambers at ambient temperature and 4
°C above ambient temperature showed evidence of temperature acclimation, but photosynthesis did not increase in response to
the 4 °C warming. On the contrary, photosynthetic rates measured at the prevailing chamber temperature throughout three growing
seasons were similar, or lower (12% lower on average) in saplings maintained at 4 °C above ambient temperature compared with
saplings maintained at ambient temperature. However, the long-term photosynthetic temperature optimum for saplings in the
field experiment was higher than it was for seedlings in either the 27 or the 31 °C growth chamber. Respiratory acclimation
was also evident in the saplings in the field chambers. Saplings had similar rates of respiration in both temperature treatments,
and respiration showed little dependence on prevailing temperature during the growing season. We conclude that photosynthesis
and respiration in sugar maple have the potential for physiological acclimation to temperature, but exhibit a low degree of
genetic adaptation. Some of the potential for acclimation to a 4 °C increase above a background of naturally fluctuating temperatures
may be offset by differences in water relations, and, in the long term, may be obscured by the inherent variability in rates
under field conditions. Nevertheless, physiologically based models should incorporate seasonal acclimation to temperature
and permit ecotypic differences to influence model outcomes for those species with high genetic differentiation between regions.
Keywords:
acclimation, adaptation, climatic warming, global change, photosynthesis, respiration, sugar maple.
