Phenology of high- and low-density wood deciduous species responds differently to water supply in tropical semiarid regions

Abstract

Although seasonal rainfall is the main factor regulating plant phenology in the dry tropics, some species flush and flower during the dry season. This apparent paradox was investigated in woody species in semiarid Brazil. A total of 500 mm of water was supplied to three 100 m2 plots along 12 weeks from the beginning of the dry season, when the photoperiod was the shortest. Six deciduous high wood density species (HWD; ≥ 0.5 g cm−3) that had flushed and flowered during the rainy season, had low water potentials (<−3.5 MPa) and shed their leaves in the control plots during the dry season, while in the irrigated plots their water potential was higher (−1.0 MPa), leaves were retained longer, and they flushed and/or flowered again. In both irrigated and control areas, four deciduous low wood density species (LWD) behaved similarly: they shed their leaves at the end of the wet season, maintained a relatively high-water potential (>−0.3 MPa) throughout the dry season and flushed and flowered at the end of this season, when the photoperiod was greater than 12 h. We conclude that the phenophases of HWD species are regulated by water availability and those of LWD species by the photoperiod.