Developmental strategies of Koenigia islandica, a high-arctic annual plant

Seed germination, growth and flowering of the arctic-alpine annual Koenigia islandica were studied in controlled environment. Intact (unabraded) seeds germinated poorely at temperatures up to 18 degrees C, with an optimum at 24 degrees C (89% in 10 d). Scarified seeds germinated rapidly, and reached 100% germination in 3 d at 21 degrees C, but no > 40% germination occurred at 9 and 12 degrees C. Thr seeds had no light requirement For germination, nor did fluctuating temperatures improve germination. Dry matter production was optimal at 12 degrees C in both short day (SD) an d long day (LD) conditions, but was markedly higher in LD than in SD at ide ntical fluences at all temperatures except 21 degrees C where the plants sh owed symptoms of severe heat stress. The temperature compensation point for net productivity was estimated to 24 degrees C, and negative carbon balanc e at higher temperatures might be an important physiological mechanism limi ting the distribution of K. islandica in Scandinavia. Flowering was extremely rapid and independent of daylength, even in a high- arctic population from 79 degrees N. In full summer daylight anthesis was r eached 24 d after germination and seeds ripened after 36 d at 15 degrees C. Days to anthesis varied little across the temperature range from 6 to 21 d egrees C, giving a linear decrease in the heat-sum requirement for the atta inment of flowering with decreasing temperature. It is concluded that conservative seed germination strategy, tininess and r apid development. low temperature optima for growth and reproduction, and d aylength indifference of flowering are important adaptations For success of an annual plant in high-arctic and high-alpine environments. Daylength neu trality has facilitated the wide-latitudinal distribution of K. islandica, including the penetration of the species to the southern hemisphere.