A. Polle

Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO2
Finzi, A.C., R.J. Norby, C. Calfapietra, A. Gallet-Budynek, B. Gielen, W.E. Holmes, M.R. Hoosbeek, et al. 2007. “Increases in Nitrogen Uptake Rather Than Nitrogen-Use Efficiency Support Higher Rates of Temperate Forest Productivity under Elevated CO2”. Proc. Nat. Acad. Sci. 104: 14014-19. http://www.pnas.org/cgi/content/abstract/0706518104v1.