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(American Journal of Botany. 2009;96:542-544.) doi: 10.3732/ajb.0800144 © 2009 Botanical Society of America, Inc.

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Limitations within "The Limits to Tree Height"¹

School of Biotechnology and Biomedical Science, University of New South Wales, Sydney, N.S.W. 2052, Australia

ABSTRACT

Koch et al. (Nature 428: 851–854) measured various parameters that were thought to limit the height of Sequoia sempervirens from northern California and concluded that the maximum height for this species is 122–130 m because within this range: (1) Irreversible embolism formation was proposed to occur when the xylem pressure was less than –1.9 MPa. (2) The leaf mass to area ratio exponentially approached 833 gxm^–2. (3) The discrimination against ¹³CO₂ exponentially approached –20. (4) Light-saturated photosynthesis per unit leaf mass decreased to zero, indicating no net gain in leaf biomass. These conclusions are questioned here by reassessing the assumed limits to the biophysical parameters and by reexamining the proposed linear and exponential relationships between these parameters and tree height. It is concluded that: (1) Embolism repair mechanisms could have occurred at –2.7 MPa. (2) The leaf mass to area ratio could be a result of, rather than a determinant of, the large differential between cellular turgor and the xylem pressure. (3) The discrimination against ¹³CO₂ may show two populations of foliage with apparent linear relationships with height rather than one exponential relationship. (4) The light-saturated photosynthesis per unit leaf mass as a measure of biomass investment in leaf expansion excludes investment in branch and trunk wood. As a result, tree height may be limited by a long-term balance between dieback and continued growth.

Key Words: carbon isotope discrimination • hydraulic failure • limits to tree height • photosynthesis per unit leaf area • predawn turgor

Received for publication 23 April 2008. Accepted for publication 10 August 2008.

FOOTNOTES

Note: A response to this article can be found in this issue at Koch, G. W., and S. C. Sillett. 2009. A response to: Limitations within "The Limits to Tree Height" American Journal of Botany 96: 545-547.

² E-mail: AndrewGNetting{at}hotmail.com

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				G. W. Koch and S. C. Sillett A response to: Limitations within "The Limits to Tree Height" Am. J. Botany, February 1, 2009; 96(2): 545 - 547. [Abstract] [Full Text] [PDF]