AOBPreview originally published online on February 13, 2008
Annals of Botany 2008 101(5):727-736; doi:10.1093/aob/mcn013
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Effects of Light and Nutrient Availability on Leaf Mechanical Properties of Plantago major: A Conceptual Approach
Section of Plant Ecology and Biodiversity, Institute of Environmental Biology, Utrecht University, PO Box 800.84, 3508TB, Utrecht, The Netherlands
* For correspondence. Present address: Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia. E-mail yonoda{at}bio.mq.edu.au
Received: 28 September 2007 Returned for revision: 11 December 2007 Accepted: 7 January 2008 Published electronically: 13 February 2008
Background and Aims: Leaf mechanical properties, which are important to protect leaves against physical stresses, are thought to change with light and nutrient availabilities. This study aims to understand phenotypic changes of leaf mechanical properties with respect to dry mass allocation and anatomy.
Methods: Leaf lamina strength (maximum force per unit area to fracture), toughness (work to fracture) and stiffness (resistance against deformation) were measured by punch-and-die tests, and anatomical and physiological traits were determined in Plantago major plants grown at different light and nutrient availabilities. A conceptual approach was developed by which punch strength and related carbon costs can be quantitatively related to the underlying anatomical and morphological traits: leaf thickness, dry-mass allocation to cell walls and cell-wall-specific strength.
Key Results: Leaf lamina strength, toughness and stiffness (all expressed on a punch area basis) increased with light availability. By contrast, nutrient availability did not change strength or toughness, but stiffness was higher in low-nutrient plants. Punch strength (maximum force per unit punch area, Fmax/area) was analysed as the product of leaf mass per area (LMA) and Fmax/leaf mass (= punch strength/LMA, indicating mass-use efficiency for strength). The greater strength of sun leaves was mainly explained by their higher LMA. Shade leaves, by contrast, had a higher Fmax/leaf mass. This greater efficiency in shade leaves was caused by a greater fraction of leaf mass in cell walls and by a greater specific strength of cell walls. These differences are probably because epidermis cells constitute a relatively large fraction of the leaf cross-section in shaded leaves. Although a larger percentage of intercellular spaces were found in shade leaves, this in itself did not reduce ‘material’ strength (punch strength/thickness); it might, however, be important for increasing distance between upper and lower epidermis per unit mass and thus maintaining flexural stiffness at minimal costs.
Conclusions: The consequences of a reduced LMA for punch strength in shaded leaves was partially compensated for by a mechanically more efficient design, which, it is suggested, contributes importantly to resisting mechanical stress under carbon-limited conditions.
Key words: Cell walls, cost–benefit, defence, leaf biomechanics, leaf mass per area, nitrogen, Plantago major, punch-and-die test, stiffness, strength, toughness
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