Leaf and floral heating in cold climates: do sub-Antarctic megaherbs resemble tropical alpine giants?

Abstract

High latitude and altitude floras are characterized by low-statured, small, wind-pollinated plants, which mainly reproduce by self-pollination or asexual reproduction. However, at odds with this are some sub-Antarctic islands that have plant species with giant growth forms and large, brightly coloured flowers which require insect visitation for pollination. The size, colour and shape of the inflorescences and leaves of these megaherbs suggest thermal benefits similar to giant tropical alpine plants of equatorial Africa, South America and Hawaii. We evaluated whether heating occurs in sub-Antarctic megaherbs, and to what extent it is related to environmental variables. We measured leaf and inflorescence temperature in six sub-Antarctic megaherb species on Campbell Island, latitude 52.3°S, New Zealand Biological Region. Using thermal imaging techniques, in combination with measurement of solar radiation, ambient air temperature, wind speed, wind chill and humidity, we assessed environmental influences on leaf and floral heating. We found that leaf and inflorescence temperatures of all megaherbs were higher than simultaneously measured ambient temperatures. Greatest heating was seen in Pleurophyllum speciosum, with observed leaves 9°C higher, and inflorescences nearly 11°C higher, than ambient temperature. Heating was highly correlated with brief, unpredictable periods of solar radiation, and occurred most rapidly in species with hairy, corrugated leaves and darkly pigmented, densely packed inflorescences. This is the first evidence that floral and leaf heating occurs in sub-Antarctic megaherbs, and suggests that leaf hairiness, flower colour and shape could provide thermal benefits like those seen in tropical alpine megaherbs.

• Campbell Island
• flower colour
• thermal imaging
• Pleurophyllum speciosum.

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Acknowledgements

We thank the New Zealand Department of Conservation, South and Eastern South Island Region, for permits and logistic support on Campbell Island; Henk Haazen, Captain of Tiama and Captain and crew of HMNZS Otago for transport; Vickey Tomlinson and Lynne Huggins for help in the field; Chris Cornwall for commenting on the manuscript. We acknowledge the University of Otago Maori Doctoral Scholarship for financial support. All thermal image and probe data, environmental measurements and thermal information are archived in the PANGAEA information system, an Open Access library aimed at archiving, publishing and distributing georeferenced data from earth system research (https://doi.pangaea.de/10.1594/PANGAEA.862013).

Notes

To access the supplementary material for this article, please see the supplementary files under Article Tools, online.