Perring, Michael, Lars Hedin, Simon Levin, Megan McGroddy, and Claire Mazancourt. 2008. “Increased Plant Growth from Nitrogen Addition Should Conserve Phosphorus in Terrestrial Ecosystems”. Proceedings of the National Academy of Sciences 105: 1971–1976. Referenced from www.pnas.org: Increased plant growth from nitrogen addition should conserve phosphorus in terrestrial ecosystems.