THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA

Abstract

SUMMARYThis paper describes the effects of transplantation on the ultrastructure and storage body distribution patterns in two saxicolous lichens which show a mutually exclusive distribution pattern. Umbilicaria vellea (L.) Ach., which grows in a snow-free microhabitat, was transplanted into an adjacent habitat which received a deep winter snow cover and which supported populations of Umbilicaria deusta (L.) Baum. The reverse was done for U. deusta in the [/. vellea habitat.Effects of transplantation on storage body distribution were evident for U. vellea, but not for U. deusta. At the ultrastructural level, thalli of U. vellea showed clear signs of disruption including senescence of the algal cells and an increase in the amount of stored starch which was negatively correlated with a decline in photosynthesis in the same replicates. Lipid deposits in U. vellea viere^ initially few in number and did not change as a result of transplantation. Changes were not observed for either species in the number of pyrenoglobuli in the pyrenoid body. Algal cells of U. deusta contained significantly larger amounts of starch and lipid than those of U. vellea and no overwintering treatment disrupted the fine structure of the plant. However, numbers of starch grains declined seasonally while thalli were under snow. Storage body distribution was found to be a stable feature of the algal cells and not dependent on short-term fluctuations in net photosynthesis. It is possible that U. deusta accumulates large amounts of photosynthetic products in the autumn and uses these to maintain low metabolic levels during the winter. It may be that U. vellea is excluded from snow-covered habitats because its thalli lack the ability to store photosynthetic products and have a pattern of gas exchange unsuited to overwintering under deep snow.

THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA

“…On the basis of the present results, and those presented previously (Scott & Larson, 1985, 1986, we conclude that U. deusta, which stores large amounts of starch and lipid, sequesters photosynthetic products for use over the winter months when its gas exchange is dominated by respiration. The large /j^iax values for thalli collected prior to the overwintering simulation, combined with high numbers of starch grains in algal cells for autumn and winter seasons (Scott & Larson, 1986) indicate that respiratory substrate is stored prior to snowfall then used up during the four months of wet, dark, relatively warm conditions under the snow pack.…”

“…Consequently, it is still capable of fixing substantial amounts of carbon when it emerges from the snow pack in the spring. Previous results (Scott & Larson, 1986 suggest that large pools of starch and other compounds may act as a respiratory substrate during the winter, allowing a positive carbon balance to be maintained over the entire year. The response of U. deusta to the other two freezing treatments confirms both field observations (Scott & Larson, 1985), and earlier experimental work (Larson, 1982), in which rates of net COg exchange were either unchanged or slightly higher than control samples.…”

“…The large /j^iax values for thalli collected prior to the overwintering simulation, combined with high numbers of starch grains in algal cells for autumn and winter seasons (Scott & Larson, 1986) indicate that respiratory substrate is stored prior to snowfall then used up during the four months of wet, dark, relatively warm conditions under the snow pack.…”

“…Reports of earlier experiments (Kallio & Heinonen, 1971;Kappen & Lange, 1972;Larson, 1982) had suggested that U. vellea was sensitive to frost damage, although the experiments were often of too long duration (nine months) to be directly relevant to the field. Field and laboratory studies also suggested that U. vellea failed to store photosynthetic products (starch and lipid) in algal cells prior to overwintering (Scott & Larson, 1985, 1986. Thus insufficient respiratory reserves were available to enable U. vellea to withstand three months in the U. deusta habitat where a low level of dark respiration would be occurring under the snow pack.…”

Three-dimensional quantitative description of symbiont ultrastructure within the algal layer oftwo members of the lichen family Umbilicariaceae

“…In quantifying cellular organelles and structures in lichens one currently faces not only a paucity of preliminary studies that might give a general idea of some basic stereological parameters (such as volume density, Vv, and surface density, Sv), but also the necessity of fine-tuning sampling and measurement methods. Ultrastructural studies of lichens in the family Umbilicariaceae carried out by Ascaso et ah (1985Ascaso et ah ( , 1986, Scott & Larson (1986) and Eversman & Sigal (1987) represent a first step in quantification, although limited to two-dimensional morphometric determinations. The use of stereological techniques to study lichen ultrastructure, allowing three-dimensional estimation of quantitative data, began with a study of the photobiont of two lichens in the family Umbilicariaceae (Ascaso & Valladares 1991).…”