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A New Method of Measuring Lichen Respiration: Response of Selected Species to Temperature, pH and Sulphur Dioxide

In the last 15 years much attention has been focussed on the physiological activities of lichens notably on aspects of inorganic nutrition and photosynthesis. Refined techniques have been developed for some of these studies dependent on the use of lichen thallus discs and radioactive tracers (Smith, 1962; Smith & Drew, 1965). Manometric and other techniques have been used for many years to study photosynthesis and respiration in lichens (Smyth, 1934; Stalfelt, 1936; Butin, 1954; Quispel, 1960; Ried, 1960a, b ; Smith, 1960; Pearson & Skye, 1965). Most of these techniques are not particularly sensitive and require the use of moderately large, not easily reproducible, amounts of lichen tissue. Results scattered through the literature afford, therefore, little more information than basic photosynthetic or respiration rates for a few lichen species. Furthermore the conditions under which these measurements have been made are extremely variable and the precise conditions with regard for instance to water content of thallus, are often omitted or not given in full. The use of an oxygen electrode to measure oxygen uptake polarographically is reported in this paper and the advantages of the method are discussed. A preliminary survey of the respiration rates of selected lichens was made under varying conditions of temperature, pH and concentration of sulphur dioxide in solution. The lichens were selected, to some extent, on the basis of their different responses in the field to varying levels of atmospheric sulphur dioxide. The recent ecological and distributional studies around centres of environmental pollution, i.e. large industrial areas, allow such selection (Jones, 1952; Fenton, 1964; Gilbert, 1965, 1968,1970; Brodo, 1966; Laundon, 1967; Skye, 1968; Hawksworth & Rose, 1970; see also bibliography in Hawksworth, 1971). Few of these workers investigated the effects of sulphur dioxide on lichen metabolism. The only reports in the literature on this subject relate to effects on the chlorophyll content of lichens and lichen algae (Rao & Le Blanc, 1966); to effects on photosynthesis and to some extent on respiration (Pearson & Skye, 1965); and to the accumulation of 'sulphur' in specimens of Parmelia saxatilis at varying distances from a centre of pollution (Gilbert, 1965; 1969). The need for data on the response of fundamental metabolic processes in lichens, e.g. respiration, to sulphur dioxide pollution is clear.