This is the link of which I was asking: http:// news.stanford.edu/news/2002/december11/jasperplots-124.html. Stanford Report, December 11, 2002. The title can be misleading because the study shows that increased CO2 when heat, water, and nitrogen are added, doesn't increase growth by as much as if CO2 wasn't increased. It's a lower rate of increase.
High carbon dioxide levels can retard plant growth, study reveals
BY MARK SHWARTZ :"The three-factor combination of increased temperature, precipitation and nitrogen deposition produced the largest stimulation [an 84 percent increase], but adding carbon dioxide reduced this to 40 percent," Shaw and her colleagues wrote.
The mean net plant growth for all treatment combinations with elevated carbon dioxide was about 4.9 tons per acre -- compared to roughly 5.5 tons per acre for all treatment combinations in which carbon dioxide levels were kept normal. However, when higher amounts of carbon dioxide gas were added to plots with normal temperature, moisture and nitrogen levels, aboveground plant growth increased by nearly a third.
Why would elevated carbon dioxide in combination with other factors have a suppressive effect on plant growth? The researchers aren't sure, but one possibility is that excess carbon in the soil is allowing microbes to outcompete plants for one or more limiting nutrients...."
But this also illustrates my point about growing food for fuel that emits N2O into the air. The Study would indicate that such increases would hamper the growth rate of plants when in the presence of increased CO2.