Photoperiodic induction of synchronous flowering near the Equator

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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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Author information


  1. Biology Division, University of Kansas, Lawrence, Kansas 66045-7534, USA

    • Rolf Borchert
  2. Department of Biology, Ludwig Maximilians University, 80638 Munich, Germany

    • Susanne S. Renner
  3. Center for Research on Sustainable Agriculture CIPAV, A. A. 20591, Cali, Colombia

    • Zoraida Calle
  4. Fundacion Puerto Rastrojo, A. A. 241438, Bogotá, Colombia

    • Diego Navarrete
    •  & Patricio von Hildebrand
  5. Botany Department, Charles Darwin Research Station, Galapagos, via AP 17-01-3891, Quito, Ecuador

    • Alan Tye
  6. Conservatoire et Jardin botaniques de la Ville de Genève, Case Postale 60, CH-1292 Chambésy/GE, Switzerland

    • Laurent Gautier
    •  & Rodolphe Spichiger


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Competing interests

The authors declare that they have no competing financial interests.

Corresponding author

Correspondence to Rolf Borchert.

Supplementary information

Word documents

  1. 1.

    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.

  2. 2.

    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).

  3. 3.

    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).

Excel files

  1. 1.

    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.


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