“Diminishing returns” in the scaling of functional leaf traits across and within species groups

*Department of Plant Biology, Cornell University, Ithaca, NY 14850;
^‡Institute of Environmental and Agricultural Sciences, Estonian University of Life Sciences, Kreutzwaldi 64, EE-51014 Tartu, Estonia;
^§Department of Forest Resources, University of Minnesota, 1530 Cleveland Avenue North,St. Paul, MN 55108;
^¶Institute of Botany and Ecology, University of Tartu, EE-51005 Tartu, Estonia;
^‖Department of Biology, University of Sherbrooke, Sherbrooke, QC, Canada J1K 2R1; and
**Department of Biological Sciences, Macquarie University, Sydney NSW 2109, Australia

Edited by James H. Brown, University of New Mexico, Albuquerque, NM, and approved April 13, 2007 (received for review February 8, 2007)

Abstract

More than 5,000 measurements from 1,943 plant species were used to explore the scaling relationships among the foliar surface area and the dry, water, and nitrogen/phosphorus mass of mature individual leaves. Although they differed statistically, the exponents for the relationships among these variables were numerically similar among six species groups (ferns, graminoids, forbs, shrubs, trees, and vines) and within 19 individual species. In general, at least one among the many scaling exponents was <1.0, such that increases in one or more features influencing foliar function (e.g., surface area or living leaf mass) failed to keep pace with increases in mature leaf size. Thus, a general set of scaling relationships exists that negatively affects increases in leaf size. We argue that this set reflects a fundamental property of all plants and helps to explain why annual growth fails to keep pace with increases in total body mass across species.

Footnotes

^†To whom correspondence should be addressed. E-mail: kjn2{at}cornell.edu
Author contributions: K.J.N. designed research; E.D.C. and Ü.N. performed research; P.B.R., A.S., B.S., and I.J.W. contributed new reagents/analytic tools; and K.J.N. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

α,

slope of SMA curve (“scaling exponent”);

C.I.,

confidence interval;

log β,

Y intercept of SMA curve (“elevation”);

MD,

dry mass;

MW,

foliar water mass;

NL,

nitrogen mass;

PL,

phosphorus mass;

SA,

lamina surface area;

SLA,

specific leaf area.