Morphological plasticity of shade‐tolerant tropical rainforest tree seedlings exposed to light changes

Summary 1 Previous studies on tropical rainforest seedlings have demonstrated low physiological plasticity in shade-tolerant species in response to light, but little is known about the morphological plasticity of such species. We examined morphological traits in seedlings of 10 shade-tolerant tropical rainforest tree species grown in four combinations of high and low light (10 and 0·8% full daylight, respectively). Plasticity of each trait was quantified using coefficients of variation. 2 Plant traits varied in their plasticity, and could broadly be ranked as follows: stem form > crown traits > root form > leaf form > biomass allocation. Acclimation to an increase in light was generally greater than acclimation to a decrease in light, but crown traits showed significant changes in the high–low treatment. 3 The ranking of species according to plasticity varied depending on the trait examined. Mean plasticity across all light treatments showed no relationship with either dry mass or relative growth rate of dry mass (RGRM) across species. However, plasticity in stem mass fraction (fraction of stem to total dry mass) was negatively correlated with low-light RGRM across species. 4 Principal components analysis indicated clustering of species depending on trait plasticity. These results suggest different strategies of light response among shade-tolerant tropical tree seedlings.

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