Differential Wetting in Some Lichens and Mosses: The Role of Morphology

Abstract

The effect of morphology on water uptake was examined in eleven species of lichen and three species of moss, using a raining wind tunnel environment. Experiments were conducted using a variety of species to test for the influence of specific morphological features such as rhizines, isidia, papules, apothecia and lamellae, in the control of water uptake and storage. Experiments were also conducted to test for the effect of variation in overall morphology on water uptake in lichens and mosses. The results show that rhizines play a major role in the water relations of some species, but not in all. Apothecia in Umbilicaria muhlenbergii have no role in water uptake, nor do the surface papules of U. papulosa or the surface isidia of U. deusta, although the lamellae of U. muhlenbergii are exceedingly important. The upper and lower cortices of lichens were also shown to have a variable capacity for water absorption. The variation in the amount of time required to achieve saturation was the same in the lichens and mosses. This time varied from three minutes in P. juniperinum to over 300 minutes in Stereocaulon saxatile. Plants with a large surface area to weight ratio absorb water at an exceedingly rapid rate. Conversely, any poikilohydric plant showing a low surface area to weight ratio absorbs water very slowly. Variation in the morphology of lichens has been shown to control evaporative water loss (Larson 1979; Larson & Kershaw 1976) in a fashion similar to the way in which variation in leaf or stem morphology controls water loss in many higher plants. These studies are the only ones to date, however, that demonstrate this feature of the biology of lichens. In general, the earlier literature is composed of studies demonstrating, through a variety of techniques, that water loss and gain in lichens, and to a lesser extent in mosses, is a passive phenomenon, and that adaptations do not exist for controlling the plant's water balance (Blum 1973). The techniques used in the past to study water loss and gain tend to fall into two categories: first are immersion experiments in which lichens or mosses are either soaked thoroughly, then allowed to dry in still air (or conversely are plunged into water when dry, followed by measurement of the plant's wet weight as imbibition occurs); second are bell 007-2745/81/1-15$1.75/0 This content downloaded from 157.55.39.192 on Sun, 28 Aug 2016 04:41:35 UTC All use subject to http://about.jstor.org/terms 2 THE BRYOLOGIST [Volume 84