Étude de la plasticité phénotypique chez le Chrysanthemum leucanthemum. I. Croissance, allocation de la biomasse et reproduction

Abstract

Phenotypic plasticity was experimentally studied in plants sampled from two tetraploid populations of ox-eye daisy, Chrysanthemum leucanthemum L. Plants were cloned and ramets were grown in an outdoor garden, in two independent experiments aimed at measuring the effects of light intensity (three treatments) and nutrient level (three treatments). When plants of the same genotype were grown under different light intensities, phenotypic plasticity was high for the following characteristics: total biomass, root weight to total weight ratio, leaf area, leaf area to total weight or specific leaf weight ratio, stem height, branching, number of heads, and time of flowering and fruiting. Genotypes grown under the three nutrient levels showed less plasticity, especially for leaf-related features. Biomass allocation patterns were also measured. Generally, lower light intensities resulted in an increase of allocation to leaves and a corresponding decrease of allocation to roots. On the other hand, lower nutrient levels caused an increase of allocation to roots accompanied by a decrease of allocation to heads, but had little effects on allocation to leaf material. The effective reproductive effort (percentage of biomass allocated to mature achenes) was higher under the lowest light intensity level, but did not change significantly with nutrient levels. The results are discussed in relation to the specificity of plastic responses with respect to the nature of environmental stresses. The prolific production of heads that remained immature at the onset of cold autumn temperatures is interpreted as a nonadaptative tactic in C. leucanthemum.