Photoperiodic responses of a northern and southern ecotype of black cottonwood

Abstract

Photoperiod is an important signal controlling the onset of dormancy in perennial plants. Short days typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud. bud dormancy and other adaptive responses. Photoperiodic ecotypes have evolved in many species with large latitudinal distributions. The photoperiodic responses of two northern (53°35′ and 53°50′N) and two southern (34°10′ and 40°32′N) genotypes of black cottonwood (Populus trichocarpa Torr. & Gray) were characterized by growing trees under a range of photoperiods in the greenhouse and growth chamber. Short days induced bud set in both ecotypes. resulting in trees with fewer leaves and less height growth than trees grown under long days. Short days also enhanced anthocyanin accumulation in the northern ecotype and decreased branching of the southernmost genotype. Two aspects of the photoperiodic response were evaluated for each trail: critical photoperiod. which was defined as the longest photoperiod that elicited a short‐day response, and photoperiodic sensitivity, which was defined as the change in response per unit change in photoperiod. For each of the traits analyzed, the northern ecotype had a longer critical photoperiod and greater photoperiodic sensitivity than did the southern ecotype. The short critical photoperiod and reduced photoperiodic sensitivity of the southern ecotype resulted in a significant delay in bud set compared to that of the northern ecotype, even under a 9‐h photoperiod. Typically, photoperiodic ecotypes have been characterized as having different critical photoperiods. Ecotypic differences in photoperiodic sensitivity, however, indicate that differences in the photoperiodic response curves cannot be completely described by the critical photoperiod alone. These results also suggest that the critical photoperiod. photoperiodic sensitivity and speed of bud set have a common physiological basis. Bud set occurred earlier hi the northern ecotype primarily because bud scale leaves were initiated earlier. For one of the northern genotypes, leaf primordia that were initialed under long days subsequently differentiated into bud scale leaves after the trees were transferred to a 9‐h photoperiod. This demonstrates that primordia initiated under long days are not necessarily committed to becoming foliage leaves. The response to photoperiod did not differ appreciably between the greenhouse and growth chamber conditions that were tested.

Ecotype-dependent control of growth, dormancy and freezing tolerance under seasonal changes in Betula pendula Roth

“…Common garden studies reveal that the timing of autumn bud set and spring bud flush is correlated with the latitudinal and altitudinal origin of the trees (Pauley and Perry 1954). Consistent with this, in Populus species the critical photoperiod for growth cessation is longer in the northern than in the southern ecotypes (Howe et al 1995). In Betula species timing of bud burst in spring has been shown to vary clinally along altitudinal and latitudinal gradients (Myking and Heide 1995).…”

Frost hardiness vs. growth performance in trembling aspen: an experimental test of assisted migration

“…By moving trees north out of their local habitat, one would generally expect an increasing risk of frost damage in autumn due to delayed growth cessation (Howe et al . ). This is broadly what we found in the current study with Minnesota provenances or Alberta sources moved to more northern positions showing a delay in the timing of leaf senescence, and a lesser degree of cold hardiness than local sources.…”

Natural phenological variation in aspen (Populus tremula): the SwAsp collection

“…On the other hand, late bud flush or early bud set might be disadvantageous in the competition for resources with other trees during the short growing season that characterize northern latitudes. The timing of bud set often correlate with latitude of origin (Howe et al 1995;Frewen et al 2000), and there is strong evidence for photoperiodic control of bud set (Pauley and Perry 1954) and the involvement of phytochromes in the process (Howe et al 1995;Howe et al 1996;Olsen et al 1997;Welling et al 2002).…”