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Photoperiodic induction of synchronous flowering near the Equator


In tropical rainforests, 30–65% of tree species grow at densities of less than one individual per hectare1. At these low population densities, successful cross-pollination relies on synchronous flowering. In rainforests with low climatic seasonality, photoperiodic control is the only reliable mechanism for inducing synchronous flowering2,3. This poses a problem because there is no variation in day length at the Equator. Here we propose a new mechanism of photoperiodic timekeeping based on the perception of variation in sunrise or sunset time, which explains and predicts the annually repeated, staggered, synchronous and bimodal flowering of many tree species in Amazonian rainforests near the Equator.

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Figure 1: Seasonal variation in day length, sunrise and sunset time near the Equator.
Figure 2: Synchronous, bimodal flowering and bud break in tropical forests at low latitudes.


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Correspondence to Rolf Borchert.

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Supplementary information

Supplementary Discussion 1

This describes the sun's motion and its effect on time keeping and explains the equation of time (Fig. 3). Websites and references to more detailed descriptions are provided. (DOC 96 kb)

Supplementary Discussion 2

This describes the role of the Intertropical Convergence Zone in causing bimodal rainfall patterns at ~4 °N in northern South America and the resulting bimodal flowering periodicity of three drought-deciduous tree species (Figs. 4 and 5). (DOC 806 kb)

Supplementary Table

This shows the changes in day length, sunrise and sunset time during 20-d periods around the spring and autumn equinoxes (compare Fig. 1d, f). (DOC 50 kb)

Supplementary Data

This provides in 6 worksheets flowering observations used for calculation of mean flowering time and standard deviations for Fig. 2a (0 to 5 0S) and 2c. (XLS 60 kb)

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Borchert, R., Renner, S., Calle, Z. et al. Photoperiodic induction of synchronous flowering near the Equator. Nature 433, 627–629 (2005).

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