Germination at Extreme Temperatures: Implications for Alpine Shrub Encroachment.

Susanna E Venn,Rachael V Gallagher,Adrienne B Nicotra

doi:10.3390/plants10020327

Susanna E Venn, Rachael V Gallagher + Show 1 more

Open Access

https://doi.org/10.3390/plants10020327

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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 higher than the range of maximum temperatures modelled across the species’ geographic distribution. Our results indicate that while some shrub species germinate well at high temperatures, others are apparently constrained by an inherent seed dormancy. Shrub encroachment in alpine areas will likely depend on conditions that affect seed germination at the microsite-scale, despite overall conditions becoming more suitable for shrubs at high elevations.

Highlights

Across the arctic tundra and alpine areas of the world, woody shrub species are increasing in abundance [1,2]
The lowest temperature on the TPG in which any germination was recorded was in Epacris paludosa (11 ◦C and 11.5% mean germination) and Olearia algida (11 ◦C and 3% mean germination) (Figure 1)
The breadth of the germination niche for all species tested ranged from 11–36 ◦C, with Epacris paludosa germinating across this entire range (Figure 1)

Summary

Introduction

Across the arctic tundra and alpine areas of the world, woody shrub species are increasing in abundance [1,2]. This is partly due to the higher rate of climate warming and declines in snowpack that are occurring in these regions [3,4,5]. Overall warming temperatures in many arctic and alpine regions are providing an opportunity for shrubs to increase their overall cover abundance, expand their range, and become dominant in parts of vegetation communities from which they were previously excluded, such as herbfields and grasslands [8,9,10,11]. Recruitment via seed may play an important role in the structure and functioning of alpine systems after disturbances such as fire, which may advantage obligate seeder species more than predominantly clonal species [26,27]

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