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Canopy gradients in leaf functional traits for species that differ in growth strategies and shade tolerance

Coble, Adam P, Fogel, Marilyn L, Parker, Geoffrey G
Tree physiology 2017 v.37 no.10 pp. 1415-1425
Carpinus caroliniana, Fagus grandifolia, Liriodendron tulipifera, canopy, carbon, deciduous forests, determinate growth, indeterminate growth, leaf area, leaf development, leaf mass, leaves, nitrogen, prediction, sapwood, shade tolerance, stable isotopes, tree physiology, trees
In temperate deciduous forests, vertical gradients in leaf mass per area (LMA) and area-based leaf nitrogen (Nₐᵣₑₐ) are strongly controlled by gradients in light availability. While there is evidence that hydrostatic constraints on leaf development may diminish LMA and Nₐᵣₑₐ responses to light, inherent differences among tree species may also influence leaf developmental and morphological response to light. We investigated vertical gradients in LMA, Nₐᵣₑₐ and leaf carbon isotope composition (δ¹³C) for three temperate deciduous species (Carpinus caroliniana Walter, Fagus grandifolia Ehrh., Liriodendron tulipifera L.) that differed in growth strategy (e.g., indeterminate and determinate growth), shade tolerance and leaf area to sapwood ratio (Aₗ:Aₛ). Leaves were sampled across a broad range of light conditions within three vertical layers of tree crowns to maximize variation in light availability at each height and to minimize collinearity between light and height. All species displayed similar responses to light with respect to Nₐᵣₑₐ and δ¹³C, but not for LMA. Light was more important for gradients in LMA for the shade-tolerant (C. caroliniana) and -intolerant (L. tulipifera) species with indeterminate growth, and height (e.g., hydrostatic gradients) and light were equally important for the shade-tolerant (F. grandifolia) species with determinate growth. Fagus grandifolia had a higher morphological plasticity in response to light, which may offer a competitive advantage in occupying a broader range of light conditions throughout the canopy. Differences in responses to light and height for the taller tree species, L. tulipifera and F. grandifolia, may be attributed to differences in growth strategy or Aₗ:Aₛ, which may alter morphological and functional responses to light availability. While height was important in F. grandifolia, height was no more robust in predicting LMA than light in any of the species, confirming the strong role of light availability in determining LMA for temperate deciduous species.