Plasticity in leaf traits of 38 tropical tree species in response to light; relationships with light demand and adult stature

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Abstract
Summary: The sun–shade acclimation and plasticity of 16 functional leaf traits of 38 tropical tree species were studied in relation to their light demand, maximum adult stature and ontogenetic changes in crown exposure. Species differed significantly in all leaf traits, which explained a large part of the observed variation (average R2 = 0·72). Light had a significant effect on 12 traits and species showed a similar proportional response to light, indicating that the species ranking in trait performance is largely maintained in different light environments. Specific leaf area, leaf nutrient content and chlorophyll : nitrogen ratio showed the largest plasticity to irradiance. These traits are important for maximizing growth in different light conditions because they are closely linked to the photosynthetic capacity and carbon balance of the plant. Plasticity is generally thought to be greatest for pioneer species that occupy early successional habitats with a large variation in irradiance. This hypothesis was rejected because short‐lived pioneers showed the lowest plasticity to irradiance. An alternative hypothesis states that plasticity is largest for tall species that experience large ontogenetic changes in irradiance during their life cycle. Yet plasticity was barely related to adult stature or ontogenetic changes in crown exposure. Short‐lived pioneers that experience consistently high light levels did have low plasticity, but shade‐tolerant species that experience consistently low light levels had high plasticity. Tropical rainforest species show a large variation in plasticity. Plasticity is a compromise between many factors and constraints, and all of these may explain the observed patterns to some extent.