What was done
The authors grew carob (Ceratonia siliqua L. cv. Mulata) plants from seed in air of either 360 or 800 ppm CO2 for nine weeks at three different root temperatures and four different levels of nitrogen concentration, supplied as either nitrate or ammonium, during which time they measured various plant properties and physiological responses.

What was learned
CO2-induced increases in plant biomass ranged from 13 to 100%, depending on root temperature and nitrogen amount and source, with the greatest responses being recorded in the nitrate-fed plants.

What it means
In an attempt to give their findings a negative environmental twist, Cruz et al. say their results "highlight the potential for uncoupling biomass accumulation from increment of air CO2 concentration and show that, more than nitrogen availability, N source [our italics] may offset [our italics] positive plant growth responses under elevated CO2 and root temperature."  It is truly amazing that only two years ago, Bloom et al. (2002) were giving the very same negative twist to their finding that ammonium-fed plants recorded the greatest response to atmospheric CO2 enrichment [see our Editorial of 27 Feb 2002].  Some folks, it would appear, see negativity in any kind of change, which blinds them to seeing any prospect of progress.

Reference
Bloom, A.J., Smart, D.R., Nguyen, D.T. and Searles, P.S.  2002.  Nitrogen assimilation and growth of wheat under elevated carbon dioxide.  Proceedings of the National Academy of Sciences, USA 99: 1730-1735.