Variation in the thermal tolerance of plants at global and local scales

Speaker: Aelys M. Humphreys, Department of Ecology, Environment and Plant Science, Stockholm University.

winter landscape with some houses on the background and some patches of dry grass
Overwintering grasses. Bergius Botanic Gardens.

Temperature has long been considered one of the strongest determinants of plant distribution patterns globally. This is particularly true for cold temperatures because the physiology required to tolerate cold and freezing conditions is complex and assumed to be difficult to evolve. Yet, since their origins in the warm, wet tropics, flowering plants have clearly transitioned to temperate climates multiple times independently. Furthermore, evidence to suggest that cold tolerance can evolve relatively quickly is accumulating. I will present my ongoing research that addresses this contradiction. I will present the results of a broadscale meta-analysis of thermal tolerances across land plants, comparative studies of cold tolerance evolution in grasses, as well as findings from common garden and controlled climate experiments of grasses from geothermal areas of Iceland. These studies are united in their overarching aim to increase understanding of the extent to which the observed correlation between temperature and plant distributions is causal. The overall conclusions are that, broadly speaking, thermal tolerances do correlate with geographical distribution patterns but that historical biogeographical processes and rare evolutionary innovations have been more important for structuring thermal tolerances than local adaptation to current climates. Therefore, current temperature regimes tend to underestimate plants’ inherent abilities to tolerate thermal extremes. These findings highlight the value of coupling modelling approaches with experimentation, as well as the complexities involved in predicting plant responses to ongoing climate change.

view of river with green grass around and mountains on the background
Hengill, Iceland. Photo: Jan-Niklas Nuppenau