Journal Article

In Tropical Lowland Rain Forests Monocots have Tougher Leaves than Dicots, and Include a New Kind of Tough Leaf

Nathaniel J. Dominy, Peter J. Grubb, Robyn V. Jackson, Peter W. Lucas, Daniel J. Metcalfe, Jens-Christian Svenning and Ian M. Turner

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 9, pages 1363-1377
Published in print June 2008 | ISSN: 0305-7364
Published online April 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn046
In Tropical Lowland Rain Forests Monocots have Tougher Leaves than Dicots, and Include a New Kind of Tough Leaf

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

There has been little previous work on the toughness of the laminae of monocots in tropical lowland rain forest (TLRF) despite the potential importance of greater toughness in inhibiting herbivory by invertebrates. Of 15 monocot families with >100 species in TLRF, eight have notably high densities of fibres in the lamina so that high values for toughness are expected.

Methods

In north-eastern Australia punch strength was determined with a penetrometer for both immature leaves (approx. 30 % final area on average) and fully expanded, fully toughened leaves. In Singapore and Panama, fracture toughness was determined with an automated scissors apparatus using fully toughened leaves only.

Key Results

In Australia punch strength was, on average, 7× greater in shade-tolerant monocots than in neighbouring dicots at the immature stage, and 3× greater at the mature stage. In Singapore, shade-tolerant monocots had, on average, 1·3× higher values for fracture toughness than neighbouring dicots. In Panama, both shade-tolerant and gap-demanding monocots were tested; they did not differ in fracture toughness. The monocots had markedly higher values than the dicots whether shade-tolerant or gap-demanding species were considered.

Conclusions

It is predicted that monocots will be found to experience lower rates of herbivory by invertebrates than dicots. The tough monocot leaves include both stiff leaves containing relatively little water at saturation (e.g. palms), and leaves which lack stiffness, are rich in water at saturation and roll readily during dry weather or even in bright sun around midday (e.g. gingers, heliconias and marants). Monocot leaves also show that it is possible for leaves to be notably tough throughout the expansion phase of development, something never recorded for dicots. The need to broaden the botanist's mental picture of a ‘tough leaf’ is emphasized.

Keywords: Dicots; fracture toughness; herbivory; leaves; monocots; punch strength; tropical rain forest

Journal Article.  9428 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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