Photosynthesis of lichens from lichen-dominated in the alpine/nival belt of the Alps

Research project P 14437 Photosynthesis of lichens from lichen-dominated communities in the alpine/nival belt of the Alps Roman TÜRK 08.05.2000 The photosynthetic productivity and the factors affecting it will be measured in the nival zone of the Alps. In this area lichens can compose up to 50% of the ground cover and are important members of the vegetation. Although there has been extensive research on the photosynthesis and carbon balance of lichens in other cold and extreme environments, such as the Antarctic and Arctic, there have been few studies in the alpine habitats. It is proposed to use a unique research site, Sonnblick Observatory, Hohe Tauern, Austria, where suitable facilities to support microclimatic and advanced ecophysiological research coincide with a full meteorological station with a long and continuous record. Preliminary studies have shown that modern gas-exchange equipment and microclimate loggers work effectively in the area and that the carbon dioxide exchange of the lichens can be effectively measured. Over three years, it is planned to obtain diel (24 hour) patterns of CO2 exchange for several lichen species whilst recording environmental factors such as light and temperature and lichen water content. This will include studies when the lichens are buried in snow, a situation where they can possibly be very productive since many species can rehydrate and become active even when continuously frozen. Whilst these records will show the lichen response over the year they can most easily be interpreted when the photosynthetic ability of individual lichens is well known. To achieve this the response of each species to light intensity, temperature, thallus water content and humidity will be determined under fully controlled conditions in the laboratory. These responses will be measured at several times through the year and will demonstrate any seasonal acclimation in photosynthetic ability that might occur. The final aim is to achieve an initial carbon balance model for the lichen species. This will be aided considerably by the deploying of a continuously recording chlorophyll fluorescence system that will provide activity data for one lichen species on a better than hourly basis throughout the year. At the end we should have a good idea of the primary limiters to lichen productivity in the nival zone and also an idea of the more productive periods during the year. This will not only allow initial estimates to be made of the contribution of the lichens to the overall productivity of the community but also contribute to our understanding of how to best protect and conserve these communities.

The alpine/nival belt of high mountains is an extreme environment in term of low temperature, high radiation, low water availability and high wind. The vegetation of this zone is dominated by cryptogams, expecially lichens. To find out how this organisms deal with the prevailing severe climatic conditions was the main objective of this work. Laboratory and field investigations of selected dominant lichen species were carried out at a height of 3106 m above sea level in the Austrian Alps at the summit of the Hoher Sonnblick. The results obtained under controlled conditions in the laboratory show a positive net photosynthesis (NP) in temperature range between -7 C and around 30 C. Optimal temperature of maximal NP lies below 12 C. Carbon uptake was saturated at the radiation level of 1500 mol m -2 s -1 photosynthetic photon flux density (PPFD). The maximum NP tends to be low with < 6.5 mol CO 2 kg Dry Weight s -1 . Surprisingly there are some indications that the only nival lichen (Umbilicaria virginis), which is thought to be very special to the cold habitats, is adapted to a more moderate temperature and light regime. In the field different patterns of NP were detected depending opon the thallus water content (WC). No NP was detected under dry wheather conditions (relative humidity [RH] droped down to 30 % and lichen WC to 6 % of DW) at air temperatures between 3-8 C. Maximal CO 2 uptake was detected in a mean duration of NP for 3 hours in the morning. The continous CO 2 uptake over the whole day was detected under the conditions when water supply was available during the whole day, RH was higher than 95 % and lichen WC higher than 600 % of DW. Differences in the patterns of NP were mainly caused by different growth-forms i.e. crustose, foliose and fruticose. Long term investigations were carried out by chlorophyll a fluorescence measurements. This allowed the observation of lichen microclimate and metabolic activity. Maximal lichen thallus temperature was detected in October at 36.7 C and minimal in December at -23.6 C. Temperature of wet and metabolic active lichen was between -10.4 and 21.8 C. Measurements of chlorophyll a fluorescence showed that the lichen is active the through out the year. The summer season is used best for growth and this stands in contrast to antarctic lichens, which have main growth in spring and autumn. The method of measurement is now automatised and technically improved as the two further data-loggers will start functioning very soon.