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Interactive Effects of CO2 and Nitrogen on Longleaf Pine Trees
Reference
Entry, J.A., Runion, G.B., Prior, S.A., Mitchell, R.J. and Rogers, H.H.  1998.  Influence of CO2 enrichment and nitrogen fertilization on tissue chemistry and carbon allocation in longleaf pine seedlings.  Plant and Soil 200: 3-11.

What was done
The authors grew one-year-old longleaf pine tree seedlings for 20 months in pots of high and low soil nitrogen content within open-top chambers at atmospheric CO2 concentrations of 365 or 720 ppm to determine the interactive effects of atmospheric CO2 and soil nitrogen on growth.

What was learned
Although elevated CO2 had no effect on needle or fine root biomass, high nitrogen increased the dry weights of these plant components by nearly 7- and 3-fold, respectively.  Elevated CO2, however, did increase the growth of other above- and belowground organs.  Stem biomass, for example, was 34 and 62% greater at low and high nitrogen, respectively, in the high CO2 treatment.  Elevated CO2 also increased taproot and lateral root growth by 66 and 60%, respectively, but only in the presence of high nitrogen.  In summation, elevated CO2 caused no overall change in whole-plant biomass at low soil nitrogen, but at high soil nitrogen, it increased it by 42%.  These observations suggest that longleaf pine seedlings respond favorably to atmospheric CO2 enrichment when sufficient soil nitrogen is available.

What it means
Longleaf pine tree seedlings should increase their biomass as the CO2 content of the air continues to rise.  Although the CO2-induced growth response was negligible for this species at low nitrogen levels, the increasing delivery of anthropogenic nitrogen to natural ecosystems, together with the acquisition of nitrogen from the free atmosphere by the nitrogen-fixing organisms that pervade essentially all ecosystems, will likely allow juvenile longleaf pine trees to experience growth increases nearly everywhere in the future.

Reviewed 1 October 1998