1. B. A. Hungate is in the Department of Biological Sciences and the Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, USA..
2. J. S. Dukes, M. R. Shaw, and C. B. Field are in the Department of Global Ecology, Carnegie Institution of Washington, Stanford, CA 94305, USA.
3. Y. Luo is in the Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019, USA.