Bromegrass in Alaska. II. Autumn Food-Reserve Storage, Freeze Tolerance, and Dry-Matter Concentration in Overwintering Tissues as Related to Winter Survival of Latitudinal Ecotypes
Leslie J. Klebesadel, Emeritus Professor of Agronomy
Agricultural and Forestry Experiment Station; Palmer, Alaska
Bulletin 93; May 1993 (10 pages)
Summary
The objective of this study was to acquire improved understanding of factors that influence winter survival of bromegrass (Bromus spp.) at northern latitudes. Four bromegrass strains of diverse latitudinal origins were used: (a) native Alaskan pumpelly bromegrass (B. pumpellianus Scribn.) adapted at 61° to 65°N, (b) the Alaska hybrid cultivar Polar (predominantly B. inermis Leyss. x B. pumpellianus) selected at 61.6°N, and two smooth bromegrass (B. inermis) cultivars, (c) Manchar selected in the U.S. Pacific Northwest (43° to 47°N), and (d) Achenbach originating from Kansas (34° to 42°N).
· The temperate-adapted, southern-type Achenbach was lower in dry-matter concentration in crown-rhizome tissues near onset of winter, sustained greater injury from artificial freeze stress, and survived winters much poorer than the three more northern-adapted bromegrasses.
· Manchar was less injured by modest freeze stress than Achenbach, had significantly higher dry-matter concentration in overwintering crown-rhizome tissues than Achenbach, and was vastly superior to Achenbach in winter survival. Manchar, however, was more injured by freezing and was significantly poorer in winter survival than the more northern-adapted Polar and pumpelly bromegrasses.
· The rapid pre-winter build-up of stored food reserves in pumpelly bromegrass, and slow expression of those reserves as etiolated growth when tested near
onset of winter conditions, parallels the early senescence and bleaching of foliage commonly seen in that species late in the growing season.
· The predominantly hybrid, very winter-hardy Polar does not show late-season foliar yellowing but did exhibit dormancy equal to pumpelly brome; moreover, Polar stored highest levels of food reserves, and was more tolerant of moderate freeze stress than Manchar and Achenbach.
· The superior winter hardiness of pumpelly brome and Polar in Alaska is believed due primarily to (a) higher levels of freeze tolerance in overwintering tissues than in more southern-adapted bromes (a characteristic that protects against injury during extreme cold stress), and perhaps also to some extent to (b) superior winter dormancy as indicated by slower expression (as etiolated growth) of high levels of stored food reserves; that dormancy conceivably confers better tolerance to winter temperature fluctuations in the freeze-thaw range common in this area of Alaska.
· These results provide insights into certain facets of the winter-hardening process in bromegrass strains that prepare overwintering tissues to tolerate winter stresses.
· These findings also reveal differences in pre-winter changes between northern-adapted, winter-hardy bromegrasses and more southern-adapted strains that exhibit marginal to poor winter survival in this subarctic area.