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Traits controlling shade tolerance in tropical montane trees
Elisée Bahati Ntawuhiganayo1,2, Félicien K Uwizeye1,3, Etienne Zibera1
1Department of Biology, University of Rwanda, University Avenue, PO Box 117, Huye, Rwanda.
Tree Physiology
|December 21, 2019
Summary
Tropical tree shade tolerance is determined by how plants allocate biomass (e.g., leaves, stems), not by leaf-level physiological traits. This whole-plant strategy is key to understanding forest diversity.
Area of Science:
- Ecology
- Plant Physiology
- Forest Science
Background:
- Tropical rainforests exhibit high species diversity and productivity, influenced by canopy structure and gap dynamics.
- Species-specific shade tolerance is a key factor in tropical forest complexity, but the underlying traits remain unclear.
- Understanding the variation in shade tolerance is crucial for predicting forest responses to environmental changes.
Purpose of the Study:
- To identify the plant traits controlling interspecific variation in shade tolerance among tropical montane rainforest trees.
- To differentiate the roles of whole-plant biomass allocation versus leaf-level physiological traits in determining shade tolerance.
- To assess how different radiation regimes influence these traits and shade tolerance.
Main Methods:
- Investigated a range of whole-plant and leaf traits in six tropical montane rainforest tree species.
- Grew species under three distinct radiation regimes: open sky, sparse canopy, and dense canopy.
- Analyzed biomass allocation, leaf respiration, photosynthetic light compensation point, and leaf temperature.
Main Results:
- Shade-tolerant species allocated more biomass to leaves and branches, while shade-intolerant species invested more in stems, especially under low light.
- Leaf respiration and photosynthetic light compensation point did not differ significantly with shade tolerance across radiation regimes.
- Shade-tolerant species exhibited higher leaf temperatures in open conditions due to lower transpiration and larger leaf size.
Conclusions:
- Interspecific variation in shade tolerance among tropical montane trees is primarily driven by whole-plant biomass allocation strategies.
- Physiological leaf traits related to carbon balance at low radiation do not appear to be the main drivers of shade tolerance.
- Biomass allocation patterns are a more significant factor than leaf physiology in explaining shade tolerance differences in these species.
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