Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees

Abstract

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.

Deciduousness in a seasonal tropical forest in western Thailand: interannual and intraspecific variation in timing, duration and environmental cues

“…This rainfall is unlikely to influence soil water availability for the trees, but may facilitate leaf flushing by increasing relative humidity and reducing vapour pressure deficit Myers et al 1998). Water storage within plants may also influence phenological patterns (Borchert 1994a;Borchert and Rivera 2001;Rivera et al 2002;Chapotin et al 2006). In this study, however, water storage ability was not observed to facilitate dry season leaf flushing, with the two stem succulent species (Spondias pinnata and Tetrameles nudiflora) observed to consistently flush leaves during the early wet season.…”

Environmental drivers of leaf phenology in trees of the tropical species Ficus obtusifolia

“…The long-term observation of many forest species in Costa Rica (ca. 10º N) indicates that leaf fall and bud emergence take place during the driest and warmest part of the year, coinciding with the spring equinox (Borchert, 1994a;Borchert and Rivera, 2001). …”

“…The hypothesis that DL alone is the cue to phenology has been defended several times (e.g. Borchert et al, 2005;Borchert and Rivera, 2001) but more recently Calle et al (2009) suggested that insolation near the autumn equinox, not DL, is the driver of flower phenology. Usually, it is not possible to separate the effect on leaf abscission of water deficit or DL under natural conditions, because abscission intensifies when water deficit increases and DL declines (Borchert et al, 2002).…”

Irrigação, matéria orgânica e cobertura morta na produção de mudas de cumaru (Amburana cearensis)

“…Borchert & Rivera (2001) em estudo com espécies arbóreas de caules suculentos verificaram que essas plantas permaneciam inativas do início para o meio da estação seca, até mesmo quando eram irrigadas. Concluíram que a disponibilidade de água não estava determinando a ocorrência do brotamento, e que a variação sazonal no fotoperíodo era o fator que determinava a ocorrência das fenofases vegetativas e não a disponibilidade de água no solo, mesmo em baixas latitudes, onde a variação anual do comprimento do dia é inferior a uma hora, sendo a dormência induzida e quebrada por variações no fotoperíodo de menos de 30 min.…”