| Summary: | Climate warming in sub-Arctic regions leads to shifts in plant communities and retreating glaciers. Mosses and lichens contribute to important ecosystem processes in these environments, including nitrogen fixation via their microbiome. The first objective of this dissertation was to understand the extent to which long-term warming affects bacterial communities associated with the lichen Cetraria islandica. In the same context, the bacterial community and nitrogen fixation rates associated with the moss Racomitrium lanuginosum were investigated. These species are among the most common lichen and moss species in Iceland, respectively. Paper I shows that long-term warming affects the structure and composition of the bacterial community associated with C. islandica and that this change is partly mediated via changes in the plant community. The same is true for the bacterial communities associated with R. lanuginosum, although nitrogen fixation rates are apparently not affected by warming, potentially due to warming-induced shifts in nitrogen-fixing taxa (Paper II). The second objective was to evaluate the extent to which bacterial communities of two common Racomitrium species and the underlying soil as well as the moss-associated nitrogen fixation change during primary succession and whether these changes are related to changes in moss functional traits. The bacterial community composition associated with Racomitrium mosses was correlated with the successional stage in the Fláajökull forefield, and also with moss moisture content. The bacterial communities of the underlying soil also shifted with succession and were in addition related to the moss C:N ratio. Nitrogen fixation rates did not change with time since deglaciation, but were correlated with the bacterial community structure. Meðal afleiðinga hlýnunar loftslags á norðurslóðum má nefna hörfun jökla og ýmsar gróðurbreytingar. Mosar og fléttur leggja mikið af mörkum til vistkerfislegra ferla í hinu kalda umhverfi norðurslóða, þar á meðal bindingu ...
|
|---|