CONTINUOUS MONITORING OF CO2 EXCHANGE OF LICHENS IN THE FIELD - SHORT-TERM ENCLOSURE WITH AN AUTOMATICALLY OPERATING CUVETTE

Field measurements of CO2 exchange by lichens are difficult because th ese poikilohydric organisms rely on direct hydration by rain, dew or f og. Continuous enclosure of thalli in conditioned, measurement cuvette s is, therefore, not experimentally reasonable. Porometric instruments with brief enclosure times, have proved useful for studies of lichen gas exchange but allow only spot measurements and recording is not eas ily possible for extended time periods. We describe a newly developed, automatically operating cuvette that allows long-term monitoring of l ichen photosynthetic and respiratory CO2 exchange in the held. Samples , e.g, flat stone slabs covered with epilithic lichens, are positioned on the base of the cuvette where, when the cuvette is open, they are exposed to the same environmental conditions as naturally growing thal li. Ar regular intervals (typically 30 min), an upper lid automaticall y encloses the lichen for c. 3 min in a stirred cuvette; CO2 exchange is measured using IRGA techniques and microclimate data are recorded. The successful operation of the cuvette is illustrated by means of die l time courses of CO2 exchange for selected, very different weather co nditions. (C) 1997 The British Lichen Society.