Introduction Directory UMM :Data Elmu:jurnal:E:Environmental and Experimental Botany:Vol44.Issue3.Nov2000:

Environmental and Experimental Botany 44 2000 171 – 183 Leaf variations in Elaeagnus angustifolia related to environmental heterogeneity Marı´a Guadalupe Klich Departamento de Agronomı´a, Centro de Recursos Naturales Reno6ables de la Zona Semia´rida CERZOS , Uni6ersidad Nacional del Sur, C.C. 738 , 8000 -Bahı´a Blanca, Argentina Received 3 August 1999; received in revised form 6 April 2000; accepted 10 April 2000 Abstract Elaeagnus angustifolia Russian olive is a Eurasian tree that has become naturalized and has invaded zones along watercourses in many arid and semiarid regions of the world. These habitats are characterized by vertical environmental gradients, thus trees must develop some plasticity to adapt to the wide range of site conditions. This study was undertaken to test the hypothesis that variations in leaf anatomy and morphology of E. angustifolia reflect their adaptability to the differences in the microclimate that occur within the canopy of single trees. Foliar architecture, blade and petiole epidermal and internal anatomy were examined in leaves at different canopy positions and related to environmental conditions. Upper sun-leaves are exposed to higher solar irradiance and lower air humidity and are smaller, more slender and thicker than the lower, half-exposed and shade-leaves. Color varies between the leaves at different levels, from silvery grey-green in the upper strata, to dark green in the lower one. Bicolor is more evident in half-exposed and shaded leaves. When compared with the lower half-exposed and shade-leaves, the upper leaves of E. angustifolia have a greater areole density, a higher mesophyll proportion and stomatal density. Trichomes are multicellular, pedestalled, stellate-branched or peltate and their form and density can be associated with leaf color and appearance. The slender petioles of the upper leaves have proportionally more epidermis, collenchyma and phloem and less parenchyma and xylem than those of lower leaves, when observed in transverse sections. Foliar morphological and anatomical variability in E. angustifolia may be considered an adaptive advantage that enables leaves to develop and function in habitats marked by strong variations of solar radiation, air temperature and humidity. © 2000 Elsevier Science B.V. All rights reserved. Keywords : Leaf heterogeneity; Leaf architecture; Phenotypic plasticity; Water stress; Xeromorphy; Canopy microclimate www.elsevier.comlocateenvexpbot

1. Introduction

Developmental responses to small-scale envi- ronmental heterogeneity can be important for plant adaptation Novoplansky, 1996. Leaves are the plant organs most exposed to aerial conditions and the changes in their characters have been interpreted as adaptations to specific environ- ments Fahn and Cutler, 1992. Variations in the morphological and anatomical features of leaves developed at different levels in the plants have Corresponding author. Fax: + 54-291-4541224. E-mail address : mgklichcriba.edu.ar M.G. Klich. S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 9 8 - 8 4 7 2 0 0 0 0 0 5 6 - 3 been reported for many species and related espe- cially to the amount of sun exposure or water availability. Kaufmann and Troendle, 1981; Niinemets and Kull, 1994; Smith et al., 1997. Elaeagnus angustifolia L. Russian olive is a Eurasian tree that has become naturalized, form- ing monotypic stands along the watercourses in the Rı´o Negro valleys of Argentina. This species is known for its capacity to grow over a wide range of environmental conditions. For example, seedlings are tolerant of shade and mature trees can live exposed to high light intensities Shafroth et al., 1995; Lucchesini and Mensuali- Sodi, 1996. E. angustifolia can displace native woody species and has been so successful in colonising disturbed areas and old fields, that its use is prohibited in some areas Dawson, 1990. The ability of E. angustifolia to establish, grow and invade new areas has led to investigations of the conditions that might favor its spread Shafroth et al., 1995. Visiting the invaded zone, I noticed that within clustered individuals of E. angustifolia there were variations in form and color between leaves growing at different levels in a tree. I evaluated the environmental heterogeneity within the canopy of trees growing along the Rio Negro watercourse in this dry-region. Anatomical and morphological studies were performed in order to prove if the externally observed leaf differ- ences were correlated with internal adaptations. I tested the hypothesis that variations in develop- mental responses of the E. angustifolia leaves to spatial heterogeneity are related to the ecological strategies of this invasive species.

2. Material and methods