Curtis, P.S., Vogel, C.S., Wang, X.Z., Pregitzer, K.S., Zak, D.R., Lussenhop, J., Kubiske, M. and Teeri, J.A. 2000. Gas exchange, leaf nitrogen, and growth efficiency of Populus tremuloides in a CO2-enriched atmosphere. Ecological Applications 10: 3-17.
What was done
Six genotypically different aspen (Populus tremuloides) cuttings were grown in
open-top chambers for 2.5 growing seasons in Michigan, USA, at atmospheric CO2 concentrations of 350 and 700 ppm. In addition, the trees were grown on soils containing adequate and inadequate supplies of nitrogen. In this particular paper, the authors report results pertaining to the gas exchange and biomass production of young aspen trees in response to elevated CO2 and soil nitrogen supply.
What was learned
After 2.5 years of atmospheric CO2 exposure, seedlings fumigated with air containing 700 ppm CO2 exhibited rates of net photosynthesis that were 128 and 31% greater than those of control seedlings growing on soils containing high and low nitrogen contents, respectively. Neither elevated CO2 nor soil nitrogen content, however, had any significant effects on seedling stomatal conductances. In addition, rates of dark respiration were increased by 22 and 9% in CO2-enriched seedlings growing on soils containing high and low nitrogen contents, respectively. Nonetheless, the net direction of carbon flow was into and not out of seedlings, as indicated by 34 and 13% increases in total dry mass production for seedlings growing on nitrogen-rich and nitrogen-poor soils, respectively. In addition, elevated CO2 increased seedling stem density by 23 and 13% at low and high levels of soil nitrogen, respectively.
What it means
As the CO2 content of the air rises, it is likely that aspen, which is the most widely distributed tree species in North America, will exhibit significant increases in photosynthesis and growth, with the largest increases occurring on high-nitrogen-content soils. However, even on low-nitrogen-content soils, aspen clones should increase their biomass, as indicated by the 13% increase observed in this study. Thus, regardless of soil nitrogen availability, aspen trees should grow faster and larger as the atmospheric CO2 concentration continues to increase; and these phenomena should shorten the time between harvest intervals for this species on commercial timber sites.