Influence of short-days on arctic plants during the arctic long-days

Abstract

In Godhavn (Disko Island, West Greenland) Salix glauca ssp. callicarpaea, Betula nana, Vaccinium uliginosum and Empetrum hermaphroditum in their natural habitat were darkened from 5 p.m. to 9 a.m. daily. The experiment started July 2. At this time the plants were already flowering. After 10 days of this 8-hour short-day treatment the plants showed significant physiological changes compared with the plants in the normal 24-hour long-day: the leaflets of Betula nana showed an autumnal red coloring and the heat resistance (1/2 hours heating, observation 3 days later) of all 4 plants increased by 2–8° C. The frost resistance (24 hours freezing, observation 3 days later) increased significantly in the case of Betula nana. —These experiments seem to indicate that towards the fall the seasonal increase of temperature resistance and other physiological changes in plants are due primarily to the shortening of the day length and only secondarily to the decrease of temperature. Kurztagbehandlung im sommerlichen 24 Std-Langtag führt bei arktischen Pflanzen am natürlichen Standort schon nach 10 Tagen zu einer Erhöhung der Hitzeresistenz um 2–8° C. Betula nana zeigt zudem unter Kurztagbedingungen eine um l1/2 Monate verfrüht eintretende herbstliche Rotfärbung der Blätter. Es wird daraus geschlossen, daß die gegen Herbst und Winter zu eintretenden physiologischen Veränderungen bei Pflanzen der kalten und gemäßigten Zone primär auf die Verkürzung der Tageslänge und erst in zweiter Linie auf die abnehmende Temperatur zurückzuführen sind.