Effect of temperature and pH on the early stages of interaction of compatible partners of the lichen Cladonia rangiferina (Cladoniaceae)

Reindeer lichens (such as Cladonia rangiferina) are important winter forage for caribou and reindeer and are widely distributed in northern ecosystems. Widespread lichen communities may be explained by dispersal from thallus fragments or by fungal ascospores interacting with algal cells. Since three early stages of interactions between symbionts of the lichen C. rangiferina have already been established, this study investigated the effect of three temperatures (5, 20, and 35 °C) and pH levels (4.5, 6.5, and 8.5) on the early interaction of C. rangiferina by quantifying morphological differences for three fungal (internode length, number of lateral branches, number of appressoria) and one algal (cell diameter) characters using Scanning Electron Microscopy. The results showed that the fungal characters were significantly altered by the extreme temperatures (5 and 35 °C) and the pH level produced differences in the fungal characters at pH 8.5. The alga was more tolerant of the wide temperature range than the fungus while the fungus was more tolerant of pH changes than the alga. An interaction effect by temperature and pH on the symbiont characters was also observed. The study raises questions regarding the range of conditions tolerated by other species of lichens and their symbionts.