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))

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.