| dc.description.abstract | A new soil temperature control system was developed for greenhouse experiments. The
system controlled soil temperature by circulating temperature-controlled water around
seedling containers. The system was tested for 5, 20 and 30 °C soil temperatures. Tests
showed that the system was very efficient in controlling soil temperature in the
greenhouse. The coefficient of determination between water and soil temperatures was
0.99. Average soil temperatures of all 112 pots (13.5 cm deep, 11 cm top diameter) in
each system were within ± 0.4 °C of the set values. The maximum vertical variation in
soil temperature was less than 1 °C.
To investigate soil temperature effects on ecophysiological traits, a total 1568 (392 per
species) of one-year old aspen, white spruce, black spruce and jack pine seedlings were
grown at 5, 10, 15, 20, 25, 30 and 35 °C soil temperatures in two greenhouses. At the
beginning o f the third month, net photosynthesis, stomatal conductance, mesophyll
conductance, transpiration, midday xylem water potential, water use efficiency and
specific leaf area were measured. Soil temperature significantly affected all the traits in
the four species. All the traits had a strong non-linear relationship with soil temperature
modeled using a polynomial function. The derived model showed that the traits were the
most sensitive to changes in soil temperature at 6.2, 8.9, 12.7 and 12.3 °C, and
performed the best at 19.6, 21.8, 22.4 and 26.1 °C, respectively, for aspen, white spruce,
black spruce and jack pine. All the aspen seedlings, about 40 % of jack pine, 20 % white
and black spruce seedlings survived in the 35 °C treatment. In general, aspen was the
most sensitive to low soil temperatures while black spruce was the most sensitive to high
soil temperatures. Stepwise regression analysis showed that net photosynthesis of aspen
was significantly correlated to mesophyll conductance stomatal conductance and water
use efficiency. In white spruce photosynthesis was significantly correlated to mesophyll
conductance stomatal conductance, transpiration and midday xylem water potential. For
black spruce photosynthesis was significantly correlated to mesophyll conductance
stomatal conductance, transpiration and water use efficiency. In jack pine net
photosynthesis was significantly correlated to mesophyll conductance stomatal
conductance and transpiration. Net photosynthesis had a strongly linear relationship
with mesophyll conductance when data from all the species were combined. | |
