Leaf size varies by over a 100,000-fold among species worldwide. Although 19th-century plant geographers noted that the wet tropics harbor plants with exceptionally large leaves, the latitudinal gradient of leaf size has not been well quantified nor the key climatic drivers convincingly identified. Here, we characterize worldwide patterns in leaf size. Large-leaved species predominate in wet, hot, sunny environments; small-leaved species typify hot, sunny environments only in arid conditions; small leaves are also found in high latitudes and elevations. By modeling the balance of leaf energy inputs and outputs, we show that daytime and nighttime leaf-to-air temperature differences are key to geographic gradients in leaf size. This knowledge can enrich "next-generation" vegetation models in which leaf temperature and water use during photosynthesis play key roles.
Bibliographical noteFunding Information:
We thank the following people who generously provided access to previously unpublished trait data or data otherwise unavailable from source publications: D. Ackerly, H. Cornelissen, W. Cornwell, D. Duncan, E. Garnier, L. Yulin, J. Lloyd, H. Morgan, T. Navarro, J. Oleksyn, J. Overton, O. Phillips, N. Pitman, H. Poorter, L. Poorter, C. Vriesendorp, J. Wright, and A. Zanne. J. Cooke, T. Lenz, A. Ordonez, and J. Suitch helped compile and error-check trait data. This research was funded by the Australian Research Council (grants RN0459908, DP0558411, and FT100100910) and by Macquarie University (Ph.D. scholarship supporting N.D.) and is a contribution to the AXA Chair Programme in Biosphere and Climate Impacts and the Imperial College initiative on Grand Challenges in Ecosystems and the Environment. R.V. was funded by the Spanish Ministerio de Educación y Ciencia project ECO-MEDIT (CGL2014-53236-R) and European Fondo Europeo de Desarrollo Regional funds. B.F.J. acknowledges support from the National Science Foundation (USA), grant EAR-9510015. This work originated from a working group held at Macquarie University. The leaf trait data set was compiled by I.J.W., E.A.L., and R.V.G., from literature data and data provided by S.D., R.V.G., B.F.J., R.K., M.R.L., Ü.N., P.B.R., R.V., M.W., P.W., and I.J.W. Geographic and climate data were compiled or calculated by I.J.W., E.A.L., V.M., and H.W. Statistical analyses were run by V.M. and I.J.W. The modeling component was conceived by I.C.P., N.D., and I.J.W. and run by N.D. L.S. initially suggested teaming empirical analysis with energy balance models. V.M., N.D., and R.V. created the figures. I.J.W. drafted the initial manuscript with assistance from I.C.P. All coauthors contributed to subsequent versions. The “global leaf size data set” is available as an Excel workbook in the supplementary materials.