© 1986 Heron Publishing—Victoria, Canada
Effects of atmospheric humidity and acclimation temperature on the temperature response of photosynthesis in young Larix decidua Mill.
Walter Tranquillini, Wilhelm M. Havranek and Peter Ecker
Forstliche Bundesversuchsanstalt, Außenstelle für subalpine Waldforschung, A-6020 Innsbruck, Rennweg 1, Austria / Received January 6, 1986
Summary
Larch (Larix decidua Mill.) seedlings of a low altitude (600 m) Austrian provenance were raised outdoors and acclimated in chambers for 14 to
24 days during August and September at either 8 °C and an atmospheric saturation vapor pressure deficit (ΔW) of 2.5 Pa kPa–1, or 24 °C and a ΔW of 6.2 Pa kPa–1. Subsequently, their rates of photosynthesis, dark respiration and transpiration were measured at temperatures between 5
and 30 °C with ΔW either maintained below 10 Pa kPa–1 or allowed to increase with temperature up to 38 Pa kPa–1.
Below 15 °C the photosynthetic rate of cold-acclimated plants was higher, but above 15 °C it was lower, than that of warm-acclimated
plants. Temperature acclimation caused a greater shift in the temperature optimum for photosynthesis when ΔW was kept small
than when it was allowed to increase with temperature.
When ΔW was kept small, leaf conductance of cold-acclimated plants, unlike that of warm-acclimated plants, did not increase
with temperature above 15 °C. When ΔW increased with temperature, leaf conductance of cold-acclimated plants decreased more
rapidly with temperature than that of warm-acclimated plants. Low temperature acclimation increased the rate of photosynthesis
below 15 °C without affecting leaf conductance, which indicates that there was an adaptation in leaf internal processes. Further
evidence of a metabolic adaptation to acclimation temperature is that dark respiration of cold-acclimated plants was twice
that of warm-acclimated plants at all temperatures.
