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Effects of Elevated CO2 and Temperature on Leaf Pigments in Douglas-Fir
Reference
Ormrod, D.P., Lesser, V.M., Olszyk, D.M. and Tingey, D.T.  1999.  Elevated temperature and carbon dioxide affect chlorophylls and carotenoids in Douglas-fir seedlings.  International Journal of Plant Science 160: 529-534.

What was done
Douglas-fir (Pseudotsuga menziesii) seedlings were grown for three years in sunlit controlled environment chambers at combinations of ambient (350 ppm) and elevated (530 ppm) atmospheric CO2 concentrations and ambient and elevated (ambient + 3.5°C) air temperatures to determine the effects of these variables on needle pigments in this dominant tree species of northwestern North America.

What was learned
Although there were no significant interactive effects of elevated CO2 and temperature on any sampled pigment, elevated CO2 and temperature, individually, tended to have significant and opposite effects on pigment concentrations.  Elevated CO2, for example, decreased chlorophyll a, chlorophyll b, and carotenoid contents by 19, 25, and 16%, respectively, in current-year needles, while elevated temperature increased the needle contents of these same pigments by 44, 63, and 29%, respectively.  However, neither elevated CO2 nor temperature had any measurable impact on needle concentrations of UV-absorbing compounds.

What it means
As the atmospheric CO2 concentration continues to rise, it is likely that Douglas-fir seedlings will not need to produce the same amounts of chlorophylls and carotenoids in their needles as they currently do, because of CO2-induced increases in their photosynthetic efficiency.  Thus, important resources can be allocated away from such pigments and utilized for sustaining or enhancing other processes within seedlings.  However, if temperatures rise in the future, such CO2-induced down-regulation of photosynthetic pigments may become insignificant, as elevated temperatures tend to cause increases in needle concentrations of these pigments to help dissipate excess energy.  Thus, the degree of CO2-induced reductions in photosynthetic pigments will be dependent upon air temperature, with higher pigment reductions occurring under atmospheric conditions of little or no temperature change.


Reviewed 26 July 2000