Photopériodisme et dormance chez les végétaux ligneux

Abstract

SummaryThe effect of photoperiodism upon tree growth is due to the length of the uninterrupted dark period. The temperature of the dark period plays an important role. Thus, growth of Rhus typhina continues under short. 9-hr. days when night temperature is 5°C, whereas it stops when is it raised to 12°C or above. In the case of Vitis labrusca, var. « Concord », growth is stopped by 9-hr. days when the night temperature is 17°C or above, but not when it is below 12°C. With Populas canadensis, however short days exerted their inhibitory effect even at 2°C. Short days arrest the growth in length relatively rapidly (2 weeks in many species), but leaf fall can be experimentally separated from this effect. By returning the plants to long days and by using relatively high temperatures, one can keep leaves on Rhus typhina or Robinia pseudacacia for many months, even though all the buds remain completely dormant. Photoperiodic effects are mediated by changes in the endogenous regulators of the plants (auxins, gibberellins, abseisins, cytokinins). The photoperiodic behavior of many woody species as determined by experiments performed by the author since 1957 is listed in Table I.