© 1995 Heron Publishing—Victoria, Canada
Photosynthetic and transpirational responses of red spruce understory trees to light and temperature
John D. Alexander (1), John R. Donnelly (2) and John B. Shane (2)
1. Northeastern Forest Experimental Station, P.O. Box 968, Burlington, VT 05402, USA / 2. Forestry Department, University of Vermont, Burlington, VT 05405, USA / Received July 18, 1994
Summary
Understory red spruce (Picea rubens Sarg.) trees, between 20 and 50 cm in height and 12 years or more in age, were collected from mid- and high-elevation stands
in north-central Vermont and placed in a closed-cuvette system to measure photosynthetic and transpirational responses to
photosynthetic photon flux density (PPFD) and temperature. Photosynthesis, dark respiration, transpiration and water-use efficiency
of trees from both stands responded to changes in PPFD and temperature in similar ways. Trees from both stands exhibited maximum
rates of net photosynthesis at temperatures between 15 and 20 °C, and exposure to higher temperatures resulted in reduced
rates of photosynthesis and increased rates of respiration. Net photosynthetic rates generally increased with increasing light
intensity but began to level off at 250 µmol m–2 s–1. Water-use efficiency was maximal when temperature and PPFD were at 15 °C and above 400 µmol m–2 s–1, respectively.
Keywords:
dark respiration, leaf conductance, net photosynthesis, photon flux density, Picea rubens, transpiration, water-use efficiency.
