Gas-exchange measurement of carbon fluxes in stands of Antarctic lichens and mosses
| Authors | |
|---|---|
| Year of publication | 2002 |
| Type | Article in Proceedings |
| Conference | Sborník (el. verze), Workshop on Changes of the Polar Ecosystem |
| MU Faculty or unit | |
| Citation | |
| Web | Workshop on Changes of the Polar Ecosystem |
| Field | Botany |
| Keywords | Lichen; photosynthesis; Antarctica; limiting factors |
| Description | Lichens and mosses are the most conspicuous and biologically important elements of terrestrial ecosystems of maritime Antarctica. Their principal role in carbon and nitrogen acquisition, cycling, and in soil formation processes is generally accepted, but detail knowledge of their functioning in field condition is still fragmentary. Growing interest in such research is also motivated by potential use of the vegetation responses for detection of expected long-term climate change in polar regions. The presented results are based on measurements of carbon dioxide fluxes (net photosynthetic uptake, respiratory output) in stands of fruticose lichens (mainly Usnea aurantiaco-atra and U. antarctica) and several species of mosses, which formed closed stands in the surrounding of Peruvian Base situated at the Crepin Point (Admiralty Bay, King George Island, South Shetlands). Evolution of CO2 from newly formed soil under moss carpets was also monitored. The selected plant or soil samples were periodically covered by a transparent plexiglass cuvette. Short-time changes in CO2 concentration within the cuvette were measured using a portable infrared gas analyser. In addition to the measurements of diurnal courses of CO2 exchange, several experiments focused on single-factorial dependence of carbon fluxes on irradiance, plant temperature and hydration, were done. Highest diurnal carbon gain of fruticose lichens was recorded on overcast days with low temperatures (close to zero) and with high air relative humidity (above 80%), particularly when the lichen thalli were moistened by trapped snowflakes. During sunny days, the diurnal carbon balance was seldom positive, not only due to rapid drying of the thalli, but also due to their temperature-induced high respiratory losses. Separation of the relative importance of the two crucial factors was possible by simultaneous measurements of CO2 exchange in intact and in artificially moistened lichens. Prevailing overcast weather with snowing episodes even during Antarctic summer seems to be very favourable for the lichen performance. In addition to the functional traits, some morphological peculiarities of the Usnea antarctica and U. aurantiaco-atra (dense, hair-like structures in the upper part of their thalli functioning as very efficient snow traps) are probably much helpful for survival and abundance of these species at exposed places (perpendicular rocks, stony ridges). Carbon fixation rates (calculated both per area or per plant biomass unit) were much higher in mosses than in lichens, and were less sensitive to the diurnal variation in air humidity. On the other hand, large amount of the newly fixed carbon was lost in respiratory processes, and also long-term carbon balance of moss stands was diminished by microbial decomposition of dead plant parts. |
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