© 2001 Heron Publishing—Victoria, Canada
Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees
Rolf Borchert (1) and Guillermo Rivera (2)
1. Division of Biological Sciences, Haworth Hall, University of Kansas, Lawrence, KS 66045-2106, USA / 2. Instituto Multidisciplinario de Biología Vegetal, Universidad Nacional de Córdoba, Casilla de Correo 495, 5000 Córdoba, Argentina / Received March 15, 2000
Summary
Tropical stem-succulent trees store large quantities of water in their trunks yet remain leafless during the early and mid
dry season. In contrast to most other tropical trees, bud break of vegetative buds is not induced in fully hydrated stem succulents
between the winter solstice and the spring equinox by leaf abscission, abnormal rain showers or irrigation. Vegetative buds
of leafless trees are therefore in a state of endo-dormancy similar to that of temperate perennial plants during early winter.
Highly synchronous bud break regularly occurs soon after the spring equinox, often weeks before the first rainfalls of the
wet season. These observations suggested that endo-dormancy and bud break might be induced by declining and increasing photoperiods
after the autumn and spring equinoxes, respectively. In phenological field observations, we confirmed highly synchronous bud
break after the spring equinox in many trees of five stem-succulent species in the northern and southern hemispheres. Shoot
growth of potted saplings of Plumeria rubra L. was arrested by a decline in day length below 12 h after the autumn equinox, but continued in saplings maintained in a
13-h photoperiod. Conversely, exposure to a 13-h photoperiod induced bud break of dormant apical buds in saplings and cuttings
in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic control of endo-dormancy
of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod.
At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations
in photoperiod of less than 30 min.
Keywords:
bud dormancy, phenology, tropical trees, tropical dry forest.
