Influence of light intensity and water stress on leaf surface characteristics of Cynoglossum officinale, Centaurea spp., and Tragopogon spp.

Abstract

Leaf surface characteristics of Cynoglossum officinale, Centaurea diffusa, Centaurea maculosa, Tragopogon dubius, and Tragopogon pratensis, important rangeland weeds of Canada, and effects of light intensity and water stress on these characteristics were studied using scanning electron microscopy. Both adaxial and abaxial leaf surfaces of Cynoglossum officinale were covered with long, uniseriate trichomes with extensive micropapillate sculpturing. The leaf surfaces of Centaurea diffusa and Centaurea maculosa had two types of trichomes: (i) sparsely distributed, multicellular, uniseriate trichomes with ribbon-like chloroform–ether soluble extensions at their tips and (ii) glandular trichomes. Centaurea diffusa and Centaurea maculosa cannot be distinguished on the basis of trichome morphology. No crystalline epicuticular wax was observed on Cynoglossum officinale or Centaurea spp. leaf surfaces. Cynoglossum officinale and Centaurea diffusa uniseriate trichomes became more abundant as light intensity declined. Micropapillate sculpturing on Cynoglossum officinale trichomes disappeared at low light intensities. Ribbon-like extensions at the tips of Centaurea diffusa uniseriate trichomes increased with increase in soil moisture stress. The leaf surfaces of Tragopogon dubius and Tragopogon pratensis lacked trichomes but were covered with tubular epicuticular wax. Tragopogon dubius and Tragopogon pratensis cannot be distinguished on the basis of epicuticular wax morphology. The abundance and size of epicuticular wax crystals on the adaxial leaf surface of Tragopogon pratensis declined with decrease in light intensity and increased with increase in soil moisture stress. Such plasticity of leaf surface morphology may be important in the acclimation of these species to harsh environments. Key words: epicuticular wax, light intensity, moisture stress, scanning electron microscopy, trichomes, weeds.