Format: ORAL

Aelys M. Humphreys and Jan-Niklas Nuppenau

Stockholm University, Stockholm, Sweden

Geothermal areas are formed where Earths inner heat is transported to the surface. This results in peculiar formations including fumaroles, geysers and heated soils. Geothermal areas are high stress, low diversity environments, with the main factor limiting the presence of most life there being heat. The diversity of land plants occurring on geothermally heated soils is relatively well characterised, with mosses and grasses (Poaceae) being particularly common at the hottest sites. However, the geographical origin of geothermal organisms is largely unknown, as are the effects of adapting to geothermal heat, e.g. phenological shifts or performance under cooler conditions. Here we present ongoing work on geothermal grasses from Iceland, a subarctic island where scorching geothermal areas and bitterly cold non-thermal areas occur side by side. We show for the genus Agrostis, which occurs on soils 70°C, that A. stolonifera has colonised Iceland at least twice, leading to one lineage exclusive to geothermal areas and another exclusive to non-thermal areas. In contrast, A. vinealis has colonised Iceland just once, leading to a single widespread lineage occupying geothermal and non-thermal areas alike. We further show phenotypic differences, increased heat tolerance, reduced performance under cooler conditions and a shift in flowering phenology for geothermal compared to non-thermal A. stolonifera, suggesting that geothermal A. stolonifera represents a specialised, thermophilic lineage. Finally, we study Festuca rubra, which is found on moderately warmed soils (30°C). This species showed no difference in thermal tolerance, winter survival ability or phenology in response to geothermal warming, suggesting it is adjusting plastically to the geothermal conditions. Our results highlight that responses to geothermal warming can be idiosyncratic, even among close relatives, and pave the way for further studies of both adaptations to extreme environments and responses to moderate warming, using the natural laboratory afforded by geothermal areas.