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Effects of Photoperiod on Growth of Trees

1956; University of Chicago Press; Volume: 117; Issue: 4 Linguagem: Inglês

10.1086/335918

1940-1205

R. J. Downs, H. A. Borthwick,

Seedling growth and survival studies

1. The effects of photoperiod on the growth of several tree species-American elm (Ulmus americana), flowering dogwood (Cornus florida), horse chestnut (Aesculus hippocastanum), red maple (Acer rubrum), sweet gum (Liquidambar styraciflua), tulip poplar (Liriodendron tulipifera), paulownia (Paulownia tomentosa), Asian white birch (Betula mandshurica), catalpa (Catalpa bignonioides and C. speciosa), and pine (Pinus taeda, P. virginiana, and P. sylvestris)-were investigated. 2. In general, short days induced dormancy, and long days prolonged growth. The various species differed in their response to short (8-hour) days, ranging from tulip poplar, which stopped further growth after about 10 8-hour days, to elm, which required 20 weeks of 8-hour days before the plants stopped elongating new structures. However, most of the species tested seemed to required about 4 weeks of 8-hour days before they stopped growing. At higher temperatures it took a greater number of 8-hour days to induce dormancy, and at temperatures lower than 70⚬ F. growth was inhibited even on 16-hour photoperiods. 3. Catalpa, elm, birch, red maple, and dogwood apparently can be kept growing continuously by daylengths of 16 hours, whereas paulownia, sweet gum, and horse chestnut cannot. The growth of pine seedlings is intermittent on 16-hour days, but on 14 hours they can be kept growing continuously for nearly a year. There seems to be a balance between bud formation and elongation of newly formed structures that is further illustrated by sweet gum, in which the inherent tendency to form a terminal bud is only slightly exceeded by the action of continuous light in maintaining continuous elongation. 4. The effects of different qualities of supplemental light on the growth of catalpa seedlings indicate that the same photochemical reaction controlling seed germination and flowering and growth of herbaceous plant parts also controls the onset of dormancy and the elongation of new structures of woody plants. 5. It is generally conceded that many tree species require a cold period to break the dormant condition. However, in some species, such as catalpa, full development of this cold requirement occurs gradually. Before this buildup of cold requirement reaches a level adequate to maintain dormancy, long photoperiods alone may induce the resumption of growth. In other species, such as dogwood, continuous light replaces the need for a cold period, whereas in birch the terminal bud apparently requires a cold period, but the axillary buds can be induced to resume growth by long photoperiods. 6. The dormant condition of some species appears to be centered in the leaves, since defoliation at warm temperatures will cause resumption of growth of plants like sweet gum and red maple. This is not universally the case, however, because defoliation of dormant plants of catalpa, horse chestnut, and dogwood seems to have no effect.