AOBPreview originally published online on February 13, 2003
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Annals of Botany 91: 577-584, 2003
© 2003 Annals of Botany Company
The Ratio of Leaf to Total Photosynthetic Area Influences Shade Survival and Plastic Response to Light of Green-stemmed Leguminous Shrub Seedlings
1 Centro de Ciencias Medioambientales C.S.I.C. Serrano 115 dpdo, Madrid E-28006, Spain, 2 Estación Biológica de Doñana C.S.I.C. Apartado 1056, Sevilla E-41080, Spain, 3 Departamento de Biología Vegetal I. Fac. Ciencias Biológicas. Universidad Complutense de Madrid, Madrid E-28040, Spain and 4 Estación Experimental de Zonas Aridas C.S.I.C. General Segura 1, Almería E-04001, Spain
* For correspondence. Fax: 34 915640800, e-mail: valladares{at}ccma.csic.es
Received: 8 July 2002; Returned for revision: 13 November 2002; Accepted: 27 December 2002 Published electronically: 13 February 2003
Different plant species and organs within a plant differ in their plastic response to light. These responses influence their performance and survival in relation to the light environment, which may range from full sunlight to deep shade. Plasticity, especially with regard to physiological features, is linked to a greater capacity to exploit high light and is usually low in shade-tolerant species. Among photosynthetic organs, green stems, which represent a large fraction of the total photosynthetic area of certain species, are hypothesized to be less capable of adjustment to light than leaves, because of biomechanical and hydraulic constraints. The response to light by leaves and stems of six species of leguminous, green-stemmed shrubs from dry and high-light environments was studied by growing seedlings in three light environments: deep shade, moderate shade and sun (3, 30 and 100 % of full sunlight, respectively). Survival in deep shade ranged from 2 % in Retama sphaerocarpa to 74 % in Ulex europaeus. Survival was maximal at moderate shade in all species, ranging from 80 to 98 %. The six species differed significantly in their ratio of leaf to total photosynthetic area, which influenced their light response. Survival in deep shade increased significantly with increasing ratio of leaf to total photosynthetic area, and decreased with increasing plasticity in net photosynthesis and dark respiration. Responses to light differed between stems and leaves within each species. Mean phenotypic plasticity for the variables leaf or stem specific mass, chlorophyll content, chlorophyll a/b ratio, and carotenoid to chlorophyll ratio of leaves, was inversely related to that of stems. Although mean plasticity of stems increased with the ratio of leaf to total photosynthetic area, the mean plasticity of leaves decreased. Shrubs with green stems and a low ratio of leaf to total photosynthetic area are expected to be restricted to well-lit habitats, at least during the seedling stage, owing to their inefficient light capture and the low plasticity of their stems.
Key words: Coronilla juncea, Cystisus scoparius, Genista scorpius, green stems, leguminous shrubs, light acclimation, phenotypic plasticity, Retama sphaerocarpa, shade tolerance, Spartium junceum, Ulex europaeus.