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.

虽然季节性降雨是干热带地区调节植物物候的主要因素，但有些物种在旱季会开花。这种明显的悖论在巴西半干旱的木本物种中进行了研究。在光周期最短的旱季开始的 12 周内，总共向三个 100 m ²地块供应了 500 mm 的水。六种高密度落叶树种（HWD；≥ 0.5 g cm ^-3) 在雨季冲洗和开花，水势低 (<-3.5 MPa) 并在旱季在对照地块落叶，而在灌溉地块中，它们的水势更高 (-1.0 MPa)，叶子保留的时间更长，它们会再次发红和/或开花。在灌溉区和控制区，四种落叶低木材密度树种 (LWD) 表现相似：它们在雨季结束时落叶，在整个旱季保持相对较高的水势 (>-0.3 MPa) 并冲水本季末开花，光周期大于12 h。我们得出结论，HWD 物种的物候期受可用水量的调节，而 LWD 物种的物候期受光周期的调节。