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Impacts of Elevated CO2 and Soil Nitrogen on Oak Seedlings
Maillard, P., Guehl, J.-M., Muller, J.-F. and Gross, P.  2001.  Interactive effects of elevated CO2 concentration and nitrogen supply on partitioning of newly fixed 13C and 15N between shoot and roots of pedunculate oak seedlings (Quercus robur L.). Tree Physiology 21: 163-172.

What was done
The authors grew pedunculate oak (Quercus robur L.) seedlings for three to four months in greenhouses receiving atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, seedlings were subjected to low and high nitrogen fertilization treatments.  Thus, the authors studied the effects of elevated CO2 and nitrogen fertilization on growth in young oak seedlings.

What was learned
Elevated CO2 preferentially stimulated belowground growth in seedlings growing in nitrogen-poor soil, which increased their root to shoot ratios.  However, elevated CO2 increased both the above- and below-ground biomass of seedlings growing in nitrogen-rich soil.  In fact, the CO2-enriched seedlings in the nitrogen-rich soil produced 217 and 533% more stem and coarse-root biomass, respectively, than their ambiently-grown counterparts subjected to high concentrations of soil nitrogen.  Overall, elevated CO2 enhanced total seedling biomass by approximately 140 and 30% under nitrogen-rich and nitrogen-poor soil conditions, respectively.

What it means
As the air's CO2 concentration rises, it is likely that young oak seedlings will respond by increasing their atmospheric carbon uptake to facilitate enhanced biomass production.  However, the degree of this CO2-induced growth enhancement should be much greater for seedlings growing on soils of high, as opposed to low, nitrogen content.  Nonetheless, even under low soil nitrogen conditions it is likely that rising atmospheric CO2 concentrations will favor belowground root growth of oak seedlings, which should ultimately enable them to increase their nutrient uptake and enhance their CO2-induced growth response.