| dc.description.abstract | In order to examine the effects of soil temperature on a coupled photosynthesis-stomatal
conductance model, seedlings of trembling aspen (Populus tremuloides Michx),
jack pine (Pinsu banksiana Lamb. ), black spruce (Picea Mariana (Mill) B.S.P.) and
white spruce {Picea glauca (Moench) Voss.) were grown over a wide range of soil
temperatures from 5 °C to 35 “C. Temperature, light and CO2 response curves of foliar
gas exchange were measured four months after the start of the treatment. The results
showed that the four boreal tree species had very similar cardinal soil temperatures for
key model parameters (i.e., Vcmax, Jmax). The key parameters of the model showed dual
soil temperature symmetry; below-ground and above-ground temperature symmetry, and
low and high temperature symmetry. In the below-ground and above-ground
temperature symmetry, the key model parameters responded to soil temperature in a
similar manner as to leaf temperature. For low and high soil temperature symmetry, the
symmetry was not perfect, with steeper slope at the higher-than-optimum temperature
range, which indicated the photosynthetic machinery of the four boreal trees was
suppressed more at high soil temperatures than at low soil temperatures.
The effects of soil temperature on key model parameters were modeled using
three different equations. Three equations fitted the measured key model parameters
well, but only the bio-chemical equation showed a specific pattern for the equation
parameters between the four species. Soil temperature had no effects on R^, the daytime
respiration that continues in light. It was speculated that after four months of soil
temperature treatments, the four boreal tree species acclimated to different soil
temperature conditions by optimizing allocation of nitrogen investment into different
functional photosynthetic components and balancing water use efficiency and nitrogen
use efficiency. | |
