Plasticity to an irradiance gradient in foliage attributes of a perennial monocot Iris pumila (L.): Comparison of populations from habitats of contrasting light conditions
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Magnitude and variation in leaf plasticity were quantified in two Iris pumila (L.) populations from habitats of contrasting light conditions (open dune vs wood understorey) at three light intensities (high - 110, medium - 65, and low - 29 mu mol m(-2) s(-1)). Siblings developed from hand-pollinated seeds from 13 and 15 clonal genotypes in an open and a shaded population, respectively, raised in a growth-room were scored for morphological (leaf number, leaf area, specific leaf area), anatomical (stomatal density, leaf thickness, vascular bundle number, sclerenchyma and cuticle widths) and biochemical (chlorophyll content, chlorophyll a:b ratio) traits. Morphological traits in general and SLA (projected leaf area per unit leaf dry mass) in particular were more sensitive to variation in light conditions than any other examined leaf attribute, indicating their key importance for maximizimg light-energy interception at low irradiance. Regardless of the population origin, the average plasticity (percentage trait change between two successive treatments) of morphological traits declined with decreasing irradiance, opposite to anatomical traits, particularly leaf thickness, which increased parallel to light intensity decrease. Mean plasticity variation (across-family CV) changed with light level, ranking in the following order morphological < anatomical < biochemical. A higher degree of leaf plasticity to irradiance in the shaded comparing to the open population could be the adaptive outcome of different selective history they have encountered within their natural habitats.