Another study by Duke graduate student Jacqueline Mohan showed that high CO2 at FACTS-1 also boosted the growth of tree seedlings and saplings that will form the future forest. And in a poster presentation, Elke Naumburg of Duke and David Ellsworth of Brookhaven reported a 120 percent increase in photosynthesis in red maple and sweetgum saplings.
But, Naidu's report also noted that computer models suggest continued CO2 stimulation will have a lessening impact in future years, a conclusion Schlesinger expanded on in his interview.
"One might guess that plants growing at high CO2 would drop leaves having lower concentrations of nitrogen and phosphorus in them, not because they are taking up less nitrogen and phosphorus from the soil, but because they're growing so fast that the same nitrogen and phosphorus concentrations are diluted by this higher growth rate," Schlesinger said.
When microbes then decompose those nitrogen and phosphorus diluted leaves in the soil, the net result might be less nutrients -- especially nitrogen -- that trees would need to fuel the higher demand.
"So that higher demand would not be met," he added. "Then the growth rate will slow. And the upshot of this would be that the pine forest would get to its ultimate size faster, but it won't end up being any larger then it would have been had it just grown without the extra CO2."
Another report bolsters that scenario. Duke graduate student Andrew Allen used a multivariant statistical analysis method to evaluate nitrogen levels in the decaying plant matter in FACTS-1 soils in the fall of 1997. Allen's results showed a "significant decrease" in nitrogen within the soil at treated sites.
But, undercutting the nitrogen deficit predictions, Duke postdoctoral
researcher Adrien Finzi reported that h
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Contact: Monte Basgall
Monte@dukenews.duke.edu
919-681-8057
Duke University Medical Center
4-Aug-1998