Cladonia is one of the largest and widely distributed genera of lichen-forming fungi and some form the main winter diet for northern caribou and dominate the northern peatlands. Therefore, they are an ecologically important group of lichens. The ongoing climate change of the northern regions, impose challenges for lichen growth and algal interactions in these species. As in other organisms, genetic variability and phenotypic plasticity in the resynthesis of the lichen thallus will be important for their continued survival. The goal of my thesis is to better understand the variability of the reindeer lichens in an evolutionary and ecological context. Phylogenetic reconstruction (Chapter 2) together with genetic polymorphic studies with RAPD (Chapter 3) showed a lack of monophyly for 12 of 18 species of Cladonia and significant intraspecific genetic variation within the group. Genetic variation in the obligate fungal partner must also rely on the success of the symbiont interaction, which was further studied by resynthesis experiments. In vitro resynthesis experiments of C. rangiferina (Chapter 4) examined recognition- and defense-related genes of the symbionts of C. rangiferina using quantitative Polymerase Chain Reaction (qPCR) (Chapter 5) and suggested that the communication between partners occur and the survival and reestablishment of lichens in nature is affected by the presence of the compatible algal pool. This emphasizes the importance of finding the compatible algal partner for successful lichenization and suggests that parasitism and short-term interaction with incompatible algae may be a strategy allowing the fungus to survive until it finds a compatible algal partner. These studies also make parallels between the lichen symbiosis and plant pathogenic systems and provide molecular evidence for the parasitic nature of the lichen symbiosis. The collapse of the interaction between symbionts of C. rangiferina under varying temperature and pH conditions (Chapter 6) suggests the potential effect of habitat change on the reestablishment of lichens in nature. In summary, my Ph. D. research showed the importance of genetic and symbiotic versatility in an ecologically important species, using a model species in the group Cladonia and raised new questions for other lichen symbioses relevant to their life styles and habitats.

Reindeer lichens are on a dramatic decline in Sweden, with a 71 % decrease in abundance over the last 60 years. Reindeer (Rangifer tarandus tarandus L.) management, undertaken by indigenous Sámi people, depend upon extensive winter grazing grounds with abundant reindeer lichen cover. The objective of this pilot study is to restore the ecosystem function of reindeer winter grazing in post-industrial environments, by developing an artificial dispersal program of reindeer lichen thalli. This study is performed in co-operation with the mining corp. of LKAB and in consultation with Laevas reindeer herding district. There are two components to this study: I) a comprehensive literature review of indigenous and scientific knowledge regarding reindeer winter grazing and artificial reindeer lichen dispersal; and II) a field assessment of relationships between fructiose lichen occurrence and environmental variables within a coarse grid overlapped on a mosaic of vegetation patches in various successional stages, which cover part of a 28-year old abandoned quartzite heap. My findings validate that a well-drained substrate with a thin humus layer or barren ground together with the occurrence of bryophytes (not Sphagnum spp.) had the highest abundance of fructiose lichens. In contrast, abundant organic soil layer, high soil moisture, and extensive cover of graminoids and herbs showed low abundance of fructiose lichens. I conclude that reindeer lichens are indeed present in a few findings but are still facing environmental and dispersal limitations to become abundant. These limitations can be understood in the light of moisture regimes, instability or compaction of substrate, and limitations within the colonization-pool, and are further discussed with suggested revegetation implementations.