© 1998 Heron Publishing—Victoria, Canada
Photosynthetic capacity of red spruce during winter
P. G. Schaberg (1), J. B. Shane (2), P. F. Cali (1), J. R. Donnelly (2) and G. R. Strimbeck (2)
1. Northeastern Forest Experiment Station, P.O. Box 968, Burlington, VT 05402, USA / 2. School of Natural Resources, The University of Vermont, Burlington, VT 05405, USA / Received March 12, 1997
Summary
We measured the photosynthetic capacity (Pmax) of plantation-grown red spruce (Picea rubens Sarg.) during two winter seasons (1993–94 and 1994–95) and monitored field photosynthesis of these trees during one winter
(1993–94). We also measured Pmax for mature montane trees from January through May 1995. Changes in Pmax and field photosynthesis closely paralleled seasonal changes in outdoor air temperature. However, during thaw periods, field
photosynthesis was closely correlated with multiple-day temperature regimes, whereas Pmax was closely correlated with single-day fluctuations in temperature. There was a strong association between short-term changes
in ambient temperature and Pmax during the extended thaw of January 1995. Significant increases in Pmax occurred within two days of the start of this thaw. Repeated measurements of cut shoots kept indoors indicated that temperature-induced
increases in Pmax can occur within 3 h. Although significant correlations between Pmax and stomatal conductance (gs) or intracellular CO2 concentration (Ci) raised the possibility that increases in Pmax resulted from increases in stomatal aperture, fluctuations in gs or Ci explained little of the overall variation in Pmax. Following both natural and simulated thaws, Pmax increased considerably but plateaued at only 37% of the mean photosynthetic rate reported for red spruce during the growing
season. Thus, even though shoots were provided with near-optimal environmental conditions, and despite thaw-induced changes
in physiology, significant limitations to winter photosynthesis remained.
Keywords:
photosynthesis, Picea rubens, temperature, winter thaw.
