Abstract
Aims
Black spruce (Picea mariana [Mill.] B.S.P.) and white spruce (Picea glauca [Moench] Voss.) are congeneric species. Both are moderately shade tolerant and widely distributed across North American boreal forests.
Methods
To understand light effects on their ecophysiological responses to elevated [CO2], 1-year old seedlings were exposed to 360 and 720 µmol mol -1 [CO2] at three light conditions (100, 50 and 30% of full light in the greenhouse). Foliar gas exchanges were measured in the mid- and late-growing season.
Important Findings
Elevated [CO2] increased net photosynthesis (Pn) and photosynthetic water use efficiency, but it reduced stomatal conductance and transpiration. The stimulation of photosynthesis by CO2 was greatest at 50% light and smallest at 100%. Photosynthesis, maximum carboxylation rate (Vcmax) and light saturated rate of electron transport (Jmax) all decreased with decreasing light. Elevated [CO2] significantly reduced Vcmax across all light treatments and both species in mid-growing season. However, the effect of elevated [CO2] became insignificant at 30% light later in the growing season, with the response being greater in black spruce than in white spruce. Elevated [CO2] also reduced Jmax in white spruce in both measurements while the effect became insignificant at 30% light later in the growing season. However, the effect on black spruce varied with time. Elevated [CO2] reduced Jmax in black spruce in mid-growing season in all light treatments and the effect became insignificant at 30% light later in the growing season, while it increased Jmax later in the season at 100% and 50% light. These results suggest that both species benefited from elevated CO2, and that the responses varied with light supply, such that the response was primarily physiological at 100% and 50% light, while it was primarily morphological at 30% light.
Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)
