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Effects of Elevated CO2 and Temperature on the Growth of Scots Pine and Norway Spruce Seedlings
Sallas, L., Luomala, E.-M., Utriainen, J., Kainulainen, P. and Holopainen, J.K. 2003. Contrasting effects of elevated carbon dioxide concentration and temperature on Rubisco activity, chlorophyll fluorescence, needle ultrastructure and secondary metabolites in conifer seedlings. Tree Physiology 23: 97-108.

What was done
The authors grew Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings for 50 days in computer-controlled environmental growth chambers in air of ambient or twice-ambient CO2 concentration [normal or elevated (EC) treatments] at day/night temperature combinations of 19/12C or 23/16C [normal or elevated (ET) treatments], while making a host of diverse measurements on them.

What was learned
In the words of the authors, "seedling biomass growth was promoted by ET, but EC had only slight effects on the growth parameters measured, supporting the prediction of Farrar and Williams (1991) that elevated CO2 has little effect on the growth of plants adapted to low temperature." With respect to this finding, they remark that "increased growth in response to ET probably led to increased demand for N and to increased N allocation from the 1-year-old needles to the growing parts of the plant." In addition, noting that "the optimum temperature of Asat [light-saturated leaf photosynthetic rate] increases with increasing atmospheric CO2 and intercellular CO2, because of the effect of elevated CO2 on the balance between carboxylation and oxygenation by Rubisco (Cannell and Thornley, 1998)," they report they "observed this temperature-dependent CO2 growth response in both species, with seedlings accumulating the most biomass in the combined EC + ET treatment."

What it means
If the world continues to warm, there should be significant increases in the growth rates of boreal tree species, such as Scots pine and Norway spruce; and if the air's CO2 content rises concurrently, the increases in growth should be even greater.

Cannell, M.G.R. and Thornley, J.H.M. 1998. Temperature and CO2 responses of leaf and canopy photosynthesis: a clarification using the non-rectangular hyperbola model of photosynthesis. Annals of Botany 82: 883-892.

Farrar, J.F. and Williams, M.L. 1991. The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source-sink relations and respiration. Plant, Cell and Environment 14: 819-830.

Reviewed 2 July 2003