plants Communication Germination at Extreme Temperatures: Implications for Alpine Shrub Encroachment Susanna E. Venn 1,2,* , Rachael V. Gallagher 3 and Adrienne B. Nicotra 2 1 Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia 2 Research School of Biology, Australian National University, Acton, ACT 2600, Australia;
[email protected] 3 Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia;
[email protected] * Correspondence:
[email protected] Abstract: Worldwide, shrub cover is increasing across alpine and tundra landscapes in response to warming ambient temperatures and declines in snowpack. With a changing climate, shrub encroachment may rely on recruitment from seed occurring outside of the optimum temperature range. We used a temperature gradient plate in order to determine the germination niche of 14 alpine shrub species. We then related the range in laboratory germination temperatures of each species to long-term average temperature conditions at: (1) the location of the seed accession site and (2) across each species geographic distribution. Seven of the species failed to germinate sufficiently to be included in the analyses. For the other species, the germination niche was broad, spanning a range in temperatures of up to 17 ◦C, despite very low germination rates in some species. Temperatures associated with the highest germination percentages were all above the range of temperatures present at each specific seed accession site. Optimum germination temperatures were consistently within or Citation: Venn, S.E.; Gallagher, R.V.; higher than the range of maximum temperatures modelled across the species’ geographic distribution.