Extreme Northern Acclimatization in Biennial Yellow Sweetclover (Melilotus officinalis) at the Arctic Circle
Leslie J. Klebesadel, Emeritus Professor of Agronomy
Agricultural and Forestry Experiment Station; Palmer, Alaska
Bulletin 89; September 1992 (18 pages)
biennial sweetclover when grown where it is adapted. In contrast, the behavior of mid-temperate-adapted biennial cultivars, when grown in Alaska far north of their latitude of adaptation, resembled annual sweetclover.
*The obligate biennialism and therefore rapid generational cycling of this species apparently facilitated rapid selective modification toward subarctic adaptation. That adaptation, involving a shift toward enhanced winter hardiness, permitted seed maturation during the second year of growth, thus perpetuating the adventive population for continued selection.
*Natural selection within the introduced population enabled it to regain biennial habit in an area of extremely long summer photoperiods (short nyctoperiods), relatively early termination of growing season, and very low winter temperatures.
*The Arctic-Circle strain of biennial yellow sweetclover may serve as the basis for a subarctic-adapted cultivar useful in Alaska and in other northern areas of the world.
*These results contribute to a better understanding of natural selection effects in the adaptive modification of crop plants and in the evolution of latitudinal ecotypes.
*These findings also provide insights into mechanisms that condition winter survival of plants in the Subarctic.
Summary
A population of yellow-flowered biennial sweetclover (Melilotus officinalis [L.] Lam.) persisted unattended for about 15 years in Fort Yukon, Alaska (66.6°N), just north of the Arctic Circle, before seed was collected and subsequently increased for testing at the Matanuska Research Farm (61.6°N) near Palmer, Alaska. This Arctic-Circle strain showed marked morphological and behavioral differences from more southern-adapted cultivars within the same species.
*With spring seeding, the Arctic-Circle strain produced shorter growth on smaller-diameter main stems by autumn of the seeding year, yielded less forage, and possessed more and larger crown buds than more southern-adapted cultivars.
*The Arctic-Circle strain initiated storage of food reserves earlier and, in late October, over-wintering root-crown-stem tissues were higher in dry-matter concentration, were less injured by freeze stress, and had assumed a greater degree of dormancy than the cultivars of more southern adaptation.
*The Arctic-Circle strain was vastly superior in winter survival to biennial yellow sweetclover from Canada (cultivars Yukon and Erector) and the conterminous states (cultivars Goldtop and Madrid).
*The several characteristics exhibited by the strain that evolved at Fort Yukon resemble those of typical