| dc.description.abstract | To study the physiological and growth responses of eleven Ontario provenances of
white spruce [Picea glauca (Moench) Voss] to elevated atmospheric CO2
concentrations, one-year old seedlings were grown in three greenhouses under CO2
concentrations of ambient, 530 ppm, and 700 ppm for a period 90 days. The following
physiological traits were measured after 60 and 90 days of treatment: net assimilation
rate (A), stomatal conductance (gs), transpiration (E), water-use efficiency (WUE),
and intercellular to ambient CO2 concentration ratio (C|/Ca). Shoot, root, and total
biomass and biomass allocation were also measured after 60 and 90 days of treatment.
Height and root collar diameter (RCD) data were collected after 0, 30, 60, and 90 days
of treatment.
Net CO2 assimilation was significantly enhanced by elevated [CO2 ] after 60 and
90 days of treatment despite reductions in photosynthetic capacity. Elevated [CO2 ]
also enhanced WUE and decreased gs and E after 60 days of treatment. There was
significant down-regulation of photosynthesis in response to CO2 concentration
elevation. Elevated [CO2] significantly reduced Rubisco carboxylation efficiency
(Vcmax), RuBP regeneration capacity (Jmax), and triose phosphate utilisation (TPU), but
had no significant effect on leaf respiration (Rj) or C 0 2 compensation point. Despite
its substantial influence on gas exchange, CO2 concentration did not significantly
affect seedling biomass, biomass allocation, height, or RCD. No significant CO2 x
provenance interactions were found in the gas exchange measurements. Provenance
had a significant effect on the height and RCD of the white spruce seedlings. Strong
correlations existed between gas exchange and monthly climate variables for the 11
Ontario provenances of white spruce at ambient and elevated CO2 concentrations,
suggesting adaptation of individual provenances to local climate.
The implications of CO2 response of diverse sources of white spruce seedlings on
tree improvement programs will probably be minimal. Seed sources of white spruce
in Ontario selected for superior growth characteristics in the present climate will
probably perform well in the predicted future climate. | |
