Heat accumulation in hollow Arctic flowers: possible microgreenhouse effects in syncalyces of campions ( Silene spp. (Ca
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ORIGINAL PAPER
Heat accumulation in hollow Arctic flowers: possible microgreenhouse effects in syncalyces of campions (Silene spp. (Caryophyllaceae)) and zygomorphic sympetalous corollas of louseworts (Pedicularis spp. (Orobanchaceae)) Peter G. Kevan1 Received: 10 April 2020 / Revised: 5 November 2020 / Accepted: 9 November 2020 / Published online: 18 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Near-ground temperatures strongly influence Arctic plant growth, reproduction, maturation and phenological relations with pollinators and herbivores. Those temperatures become further elevated within plant parts through passive solar heating, e.g. dish-shaped blossoms that focus insolation and heat-trapping pubescent structures. Other Arctic plants gain heat in hollow structures that possibly function as microgreenhouses. Arctic plants with hollow flowers in which intrafloral temperatures and temperature excesses (i.e. above nearby air) were recorded are Silene sorensenis and S. uralensis (Caryophyllaceae) with globose syncalyces, and Pedicularis langsdorfii and P. capitata (Orobanchaceae) with sympetalous corollas. The flowers heated passively, as microgreenhouses, in sunshine but not under cloudy conditions. Lateral orientation to insolation maximizes intrafloral heating in Pedicularis spp. Temperature excesses up to about 6 °C probably accelerate development of the plants’ reproductive organs (gynoecium, androecium, fruits, seeds) through 25% additional heat units (growing degree days above 0°C) over the High Arctics short, cool, active season. How these phenomena exacerbate the effects of climate change remains to be assessed. The micrometeorology within blossoms has excited scientific interest for several decades. The phenomenon has been recently reviewed by van der Kooi et al. (2019) who explain the various mechanisms whereby blossoms become warmed, so expanding on the ideas presented by Kevan (1970, 1989). Those studies itemize blossoms that possibly function as microgreenhouses. The blossoms are hollow and variously translucent, or have translucent structures, and have air trapped within them. Thus, incident solar irradiation transmitted through the structures is absorbed by the floral organs within, and the heat is trapped and possibly also reflected on the inside surfaces.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00300-020-02772-6) contains supplementary material, which is available to authorized users. * Peter G. Kevan [email protected] 1
School of Environmental Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada
The microgreenhouse effect has been postulated to be important in warming of catkins of Salix spp. (Salicaceae) in the Arctic (Krog 1955; Mølgaard 1982; Gauslaa 1984). It has been shown that pistillate catkins are warmer than staminate ones, and that there are sexual differences in the way heat is distributed around the catkin from the insolated to the shaded aspects (Kevan 1990). Kevan (1970,
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