Schipperges, Barbara (1994) Intraspecific variations in the ecophysiology of arctic to temperate populations of the lichen Cetraria nivalis. (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 179, (31) pp.

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Abstract

Five populations of the circumpolar arctic-alpine lichen species Cetraria nivalis were compared with respect to their CO2 gas-exchange, water relations and morphology I anatomy. The populations were sampled along latitudinal and altitudinal gradients, covering a broad range of macroclimatic conditions (from the temperate to the arctic climatic zone). The native sites were: Mount Glungezer (Austrian Alps), Vickleby-Alvar (Öland, southern Sweden), Abisko (northern Swedish Lapland), Mount Slattatjakka (northern Swedish Lapland) and Ny Alesund (Svalbard). In addition, provenances of the same origin, transplanted in 1983/84 to a site at the Scientific Research Station in Abisko (ANS), were investigated to examine possible plastic acclimations or ecotypic differentiation. CO2 gas-exchange response to light, temperature and thallus water content were measured in the laboratory and in the field by means of infrared gas analysis. Also the water relations, by means of desiccation series, water vapour uptake measurements from humid air and diurnal courses of thallus water content under different environmental conditions, were examined by combining field and laboratory measurements. Further, a microclimatological comparison of the different field sites was carried out recording the parameters photosynthetic active radiation, air temperature, relative air humidity and wind speed 30 cm above ground surface. Comparison of the microclimate at the 30 cm level with that at lichen level (2 cm above the ground) did not show significant differences during periods of lichen activity, i.e. mostly cool, moist and overcast conditions. Morpholgical/anatomical investigations on freeze-microtom sections supported some of the physiological results regarding water relations and CO2 gas-exchange of the different populations. With respect to CO2 gas-exchange parameters, water relations, chlorophyll content and some morphological and anatomical features of the Cetraria nivalis populations, two groups were defined: a "southern" group, containing the populations from Glungezer and Öland, and a "northern" group, containing the populations from Abisko, Slattatjakka and Svalbard. The transplanted Cetraria nivalis provenances showed still after 5-6 years of cultivation at ANS differences in CO2 gas-exchange response parameters (Ic, Is, Hopt, He, Tc, Topt, Pmax). Also variations in water storage capacity (Hmax) were found. These results indicate ecotypic differentiation. There was a general tendency of increasing net photosynthetic rates (expressed as mg CO2 g DW-lh-1) towards the higher latitudes. Regarding the CO2 gas-exchange response of the native populations this tendency was reverse, i.e. net photosynthetic rates (expressed as mgCO2 gDW-lh-1) were highest in the population of Öland and decreased towards the higher latitudes and altitudes. Also chlorophyll content was decreasing with latitude. An important factor for the interpretation of these gas-exchange results was therefore the choice of the relation basis (either dry weight or chlorophyll content). Obtained differences in net photosynthetic rates between the native populations when gas-exchange was expressed as mgCO2 gDW-lh-1 could partly be diminishued or eliminated if expressed as mgC02 mgChl-lh-1. This indicated a higher efficiency per unit chlorophyll of the algal photosynthetic apparatus of the subarctic and arctic populations. The CO2 gas-exchange data obtained in the field showed higher variation than those from laboratory measurements, but were generally in the same order of magnitude. The Chla/b ratio of the population from Öland was about twice as high as that of the other populations. This fact, a high light compensation point and light saturation value, a thicker cortex and a thicker algal layer suggested to be an adaptation to higher irradiances as it is found in sunleaves or sun forms of vascular plants. With respect to water relations, the subarctic and arctic populations showed a higher water storage capacity and higher water holding capacity (slower desiccation rate) than the alpine and temperate populations. This was explained by anatomical differences (thicker medulla) and by habitat differences (e.g. dryness of habitat). A productivity model for Cetraria nivalis from Abisko gained from data of the snowfree months May to September 1990, 1991 and 1992 was calculated using laboratory gasexchange data, results of field and laboratory water relation measurements and mesoclimatic data from the automatic weather station at ANS. This model shows a considerable gain of carbon in almost all months (ranging between 0.73 and 5.72 g C kg c-1), which is assumed to be necessary to balance expected respiration losses during the dark period in autumn and winter in the Subarctic and to grow. It is concluded from these results that the investigated Cetraria nivalis populations are different ecotypes. However, besides a genetical differentiation there seems to be a considerable degree of physiological plasticity, as shown in seasonal differences. The ecotypic differentiation can be interpreted on the basis of plant history, i.e. by survival of the Pleistocen galciation periods in different refugia and by re-immigration patterns after the retreat of the ice, which has resulted in the recent disjunct main distribution areas of Cetraria nivalis in different climatic regions.

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