1. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 (G.J.T., J.L.M.-S.);
2. Advanced Analytical Center for Environmental Studies, Savannah River Ecology Laboratory, The University of Georgia, Aiken, South Carolina 29801 (D.B.H., P.M.B.);
3. Purdue Rare Isotope Measurement Laboratory, Purdue University, West Lafayette, Indiana 47907–1396 (D.E.);
4. Soil Science and Plant Nutrition, Faculty of Agriculture, University of Western Australia, Perth, Western Australia 6907, Australia (Z.R.); and
5. Department of Botany, University of Adelaide, Adelaide, South Australia 5005, Australia (R.J.R.)