AOBPreview originally published online on October 27, 2005
Annals of Botany 2006 97(1):97-107; doi:10.1093/aob/mcj004
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The Leaf Size–Twig Size Spectrum of Temperate Woody Species Along an Altitudinal Gradient: An Invariant Allometric Scaling Relationship
1 Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China, 2 Department of Biology, Nanjing University, Nanjing 210093, China and 3 Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
* For correspondence. Email shcs{at}nju.edu.cn
Received: 17 June 2005 Returned for revision: 25 August 2005 Accepted: 23 September 2005 Published electronically: 27 October 2005
• Background and Aims The leaf size–twig size spectrum is one of the leading dimensions of plant ecological variation, and now it is under development. The purpose of this study was to test whether the relationship between leaf size and twig size is isometric or allometric, and to examine the relationship between plant allometric growth and life history strategies in the spectrum.
• Methods Leaf and stem characters—including leaf and stem mass, total leaf area, individual leaf area, stem cross-sectional area, leaf number and stem length—at the twig level for 59 woody species were investigated along an altitudinal gradient on Changbaishan Mountain in the temperate zone of China. The environmental gradient ranges from temperate broad-leaved mixed forest at low altitude, to conifer forest at middle altitude, and to sub-alpine birch forest at high altitude. The scaling relationships between stem cross-sectional area and stem mass, stem mass and leaf mass, and leaf mass and leaf area at the twig level were simultaneously determined.
• Key Results Twig cross-sectional area was found to have invariant allometric scaling relationships with the stem mass, leaf mass, total leaf area and individual leaf area, all with common slopes being significantly larger than 1, for three altitudinal-zoned vegetation types under investigation. However, leaf mass was found to be isometrically related to stem mass and leaf area along the environmental gradient. Based on the predictions of previous models, the exponent value of the relationship between twig cross-sectional area and total leaf area can be inferred to be 1·5, which falls between the confidence intervals of the relationship at each altitude, and between the confidence intervals of the common slope value (1·17–1·56) of this study. This invariant scaling relationship is assumed to result from the fractural network and/or developmental constraints of plants. The allometric constants (y-intercepts) of the relationships between the stem cross-sectional area and leaf area (both total leaf area and individual leaf area) were found to decrease significantly along the altitudinal gradient. This suggests that the species would support less leaf area at a given twig cross-sectional area with increasing environmental stress.
• Conclusions This study demonstrated that plants respond to the environmental gradient by changing the y-intercepts of the relationship between leaf size–twig size, while keeping the exponent value of the allometric relationship as an invariant constant. The allometric growth in the twig size–leaf size spectrum is related to many other components of plant life history strategy, including the well established life history trade-off between efficiency and safety in the hydraulic transport of water.
Key words: Allometric growth, altitudinal gradient, leaf area, stem mass, leaf mass, life history trade-off, scaling, twig cross-sectional area
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