CO 2 exchange of the endolithic lichen Verrucaria baldensis from karst habitats in northern Italy

Abstract

CO exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO concentration. The species had low CO exchange rates (maximum net photosynthesis: c. 0.45 μmol CO m s; maximum dark respiration: c. 0.3 μmol CO m s) and a very low light compensation point (7 μmol photons m s at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9-15°C. Photosynthetic activity was affected only after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant. Low photosynthetically active radiation (normally below 40 μmol photons m s), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO assimilation were often measured in the absence of condensation phenomena.

Microscale biopitting by the endolithic lichen Verrucaria baldensis and its proposed role in mesoscale solution basin development on limestone

“…Consequently, the intermittent accumulation of water in the enlarged micro‐depressions following rainfall events may inhibit gaseous exchange between the periodically submerged lichen and the atmosphere, inducing a number of physiological responses that may limit, and ultimately cause the cessation of, algal or fungal productivity. For example, water accumulation may cause the blocking of CO 2 diffusion pathways in the thallus (Palmer and Friedmann, ; Lange and Green, ; Tretiach and Geletti, ), or an alteration of the pH environment which intimately influences the nutrients available to the lichen. Ultimately, these processes may contribute to the gradual death of a terrestrial lichen, such as Verrucaria baldensis , within the troughs, leaving characteristic raised ‘islands’ of metabolizing lichen surrounded by microscale biotroughs which are up to 1 mm deep in the samples collected (Figure c).…”

“…Diagram showing the main structural components of euendolithic Verrucaria baldensis with perithecium (adapted from Tretiach and Geletti, ; Pinna et al ., ; Bungartz et al ., ; Dobson, ). Involucrellum – the external cover of the perithecium.…”

An Investigation of the Role of Water (Rain and Dew) in Controlling the Growth Form of Lichens on Cobbles in the Negev Desert

“…We speculate that on loose cobbles that tend to condense high amounts of dew, the absorption of the water by the calcite minerals assist in reducing the negative effect of the thick film of water that acts to impede efficient CO 2 diffusion into the carboxylation sites (Lange and Tenhunen 1981;Tretiach and Pecchiari 1995). By reducing the thickness of the film of water higher gain of net carbon will take place (Lange and Tenhunen 1982;Tretiach and Gelletti 1997). This may be further improved by a high concentration of CO 2 that one may expect under enhanced lichen respiration and the subsequent dissolution of the limestone (Syers and Iskandar 1973;Chen et al 2000).…”

Experimental investigations into the influence of biofilms and environmental factors on short‐term microtopographic fluctuations of supratidal sandstone

“…In comparison, no obvious surface change pattern was demonstrated on the non-colonized block with changing humidity, except for a continuous expansion occurring under NHO treatment. Consequently, the photosynthetic activity is limited by desiccation (Tretiach and Geletti, 1997), and lithobiontic biofilms only recover from dehydration and absorb water when temperature drops to a suitable range for their physiological activity. Significant surface movements were observed on the colonized rock surface under varying temperature when humidity was kept constant.…”