The Deciduous Behavior of a Tropical Plant, Plumeria acuminata

Abstract

AbstractThe deciduous behavior of the tropical perennial Plumeria acuminata Ait., cultivar Sherman White, was investigated. The temperature during the period of experiment varied only 3°C, the mean maxima and minima, respectively, being; 28.5° and 23.5°C for summer months and 25.5° and 20.6°C for winter months. The length of the day‐light period ranged from 14¼ hours on the longest day in June to 11¾ hours on the shortest day in December.Under naturally prevailing conditions of temperature and day‐lengths, cessation of leaf formation and shedding of foliage occurred during the longer‐night, autumn‐winter months. The shedding was manifested in two stages: from mid‐October to mid‐January there was a slow but steady decrease in the number of leaves per plant, and in late January there occurred an abrupt abscission of all remaining leaves. Light interruptions during the middle of each night prevented a net loss in foliage as well as the en masse shedding in late January.Stem elongation was retarded during the autumn‐winter months, but its rate was fully restored when the long nights were interrupted with artificial light. Flowering was unaffected by day‐length.On the basis of these observations it is concluded that the deciduous behavior of Plumeria and perhaps other tropicals, alike temperate climate species, is governed by photoperiod. Cessation of leaf formation and en masse shedding of foliage are induced by long nights. However, in contrast to temperate zone plants, in which deciduousness is an adaptation against the winter cold and freeze, deciduousness provides tropical plants a survival advantage, perhaps, against seasonally recurring droughts.