Is leaf heteroblasty an adaptation to shade?
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Harshi K. Gamage, Ph.D.
Linley K. Jesson, Ph.D. (Supervisor)
School of Biological Sciences, Victoria University of Wellington
and Donald R. Drake, Ph.D. (Supervisor), Present address : Department of Botany, University of Hawaii, Honolulu, USA.
Heteroblastic plants (plants that have different leaf morphologies between seedling and adult stages) are extraordinary common in New Zealand relative to other countries in the world. Heteroblastic growth could be an adaptation to changes in light environment from understory to overstory experienced by seedling and adult stages, respectively.
In this research project, Harshi Gamage selected 4 pairs of congenerichomoblastic and heteroblastic species in genera Aristotelia, Hoheria, Pseudopanax and Melicope to test whether heteroblasty is an adaptation to changes in light. She grew seedlings in deep shade and full sun light environments in a glasshouse and in the field. The field experiment was done at Karori Sanctuary.
Seedlings were planted in forest understory and existing tree-fall gaps in valley sites of the Sanctuary. After the end of the experiment whole-plant responses (foliar and growth) were measured.
Hemispherical photograph of
forest understory site
(canopy openness = 10%)
Harshi found that heteroblastic species had lower survival relative to homoblastic species in deep shade, but had 100% survival in full sun enclosures and canopy gaps. However, homoblastic species had lower survival than heteroblastic congeners in gaps. Heteroblastic species, which initially had lobed/trifoliate leaf morphology, produced entire/simple leaves in the shade, but retained their initial leaf morphology in full sun.
Hemispherical photograph of
canopy gap site (canopy openness = 70%)
Both homoblastic and heteroblastic species had plastic responses to changes in light environment, suggesting that heteroblasty is not fixed at seedling stage. However, heteroblastic species survived better than homoblastic relatives in high light. Harshi concluded that heteroblastic seedling leaf morphology is not associated with deep shade.
Papers & Presentations
- Technical Abstract, (pdf format, 104 kB).
- Graphic example (pdf format, 52 kB) showing the difference between juvenile and adult leaves for heteroblastic and homoblastic plants.
- Gamage H. K., Jesson L. K., and Drake D. R. (2005). Influence of leaf form on photosynthetic carbon gain and growth of heteroblastic seedlings to light. 22nd International Union of Forest Research Organizations (IUFRO) World Congress, 8–13 August, Brisbane, Australia.
- Gamage H. K., Jesson L. K., and Drake D. R. (2004). Why do plants change leaf morphology? Responses of homoblastic and heteroblastic seedlings to light. New Zealand Ecological Society Conference, 30 Aug-2 Sept, Invercargill, New Zealand.
- Gamage H. K., Jesson L. K., and Drake D. R. (2004). Do heteroblastic plants give up plasticity within a life stage? Plasticity of homoblastic and heteroblastic seedlings to changes in light environment. New Zealand Ecological Society Conference, 30 Aug-2 Sept, Invercargill, New Zealand.
- Gamage H. K., Jesson L. K., and Drake D. R. (2003). Leaf anatomy and stomatal conductance: Do foliar responses determine the shade-tolerance of homoblastic and heteroblastic seedlings? New Zealand Ecological Society Conference, 16-20 Nov, Auckland, New Zealand.
- Gamage H. K., Jesson L. K., and Drake D. R. (2002). Why are there so many heteroblastic plants in New Zealand flora? Shade-tolerance or shade-avoidance? Ecology 2002Conference, New Zealand and Australian Ecological Societies, 2-6 Dec, Cairns, Australia.
- Gamage H. K., Jesson L. K., and Drake D. R. (in review). Is leaf heteroblasty an adaptation to shade? Foliar responses of homoblastic and heteroblastic seedlings to sun and shade. Annals of Botany.
Glossary
- Congeneric: belonging to the same genus.
- Heteroblastic: plants that have dramatic changes in leaf size, shape and growth habit between juvenile and adult stages (see this graphic example, pdf format, 52 kB)
- Homoblastic: plants that have small changes in leaf size, shape, and growth habit between juvenile and adult stages (see this graphic example, pdf format, 52 kB)
- Morphology: the study of form or appearance of organisms (e.g., leaf size, shape, and margin).
- Plastic: An organism or genotype that varies its phenotype with environmental conditions.
Acknowledegments
This study was funded by a Targeted PhD scholarship by Victoria University of Wellington and annual field research grants awarded by the Wellington Botanical Society.
Profile
Harshi K. Gamage. Ph.D.
Ph.D. (Plant Ecophysiology) - Victoria University of Wellington.
M.Sc. (Forestry) - University of Sri Jayewardenapura, Sri Lanka.
B.Sc. (Biology) - University of Sri Jayewardenapura, Sri Lanka
Harshi is interested in the links of morphological, structural, and physiological differences at leaf level with whole plant growth and how it is advantageous for trees to change in the environment.
Published June 26, 2004
Updated July 11, 2005
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