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Effects of Elevated CO2 and Temperature on Growth of Five Boreal Trees
Reference
Tjoelker, M.G., Oleksyn, J. and Reich, P.B. 1998. Temperature and ontogeny mediate growth response to elevated CO2 in seedlings of five boreal tree species. New Phytologist 140: 197-210.

What was done
The authors germinated and grew deciduous (quaking aspen, paper birch, tamarack) and coniferous (black spruce and jack pine) seedlings for three months in controlled environment chambers with 370 or 580 ppm atmospheric CO2 at five air temperature regimes, ranging from 18 to 30C, to determine the interactive effects of these variables on early growth in these specific trees.

What was learned
Temperature had a strong impact on the CO2 growth response of seedlings, with maximal dry mass enhancements generally occurring at species optimum growth temperatures; and this phenomenon was greater at higher temperatures in deciduous vs. coniferous species. At the lowest temperature regime, however, seedling growth responses to elevated CO2 were reduced or even suppressed. Averaged across all growth temperatures, elevated CO2 increased dry mass relative to that produced in ambient CO2 by about 50% for the deciduous trees and 20% for the coniferous species. Elevated CO2 also impacted relative growth rates, with the faster growing deciduous trees exhibiting initially higher rates than those of the slower growing coniferous species. However, as the study progressed, the CO2-enhanced relative growth rates steadily declined in two of the three deciduous species, while they increased in both of the conifers, suggesting that a slow growth rate is not necessarily indicative of a limited potential for growth response to CO2.

What it means
As the CO2 content of the air increases, seedlings of all five of these species should exhibit increases in photosynthesis that will allow them to grow larger than they normally would. This positive growth phenomenon will likely occur in all but the coldest regions of their ranges, where their growth is limited by low air temperatures.


Reviewed 1 April 1999