The Role of Apical Dominance in Paradormancy of Temperate Woody Plants: A Reappraisal

Abstract

Paradormancy, also known as summer dormancy, is the temporary dormancy which precedes winter or endodormancy in temperate woody plants. Apical dominance, the control exerted by the shoot apex over the outgrowth of the lateral buds, is thought to play a primary role in the paradormancy of these current lateral buds which normally do not grow out until the following spring after over-wintering. In the present study, to test apical dominance, periodic decapitation and defoliation beginning with early spring flushing and extending through the growing season were carried out on eleven tree species (white ash, green ash, red oak, black walnut, pignut hickory, shagbark hickory, sweetgum, cottonwood, sugar maple, hybrid silver/red maple and white pine) ranging in age from 6 to 50–60 years. Significant decapitation and defoliation release of current lateral buds into growing branches was found only in silver/red hybrid maple and red oak, respectively. In a greenhouse study of 1-year-old sugar maple and green ash seedlings, a significant response was found only in the latter. The lack of response in most of the older species analyzed indicates that other inhibitory influences may be overriding that of apical dominance and suggests that apical dominance does not play the primary role in paradormancy in some temperate woody species.