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Abstract
Background : Non-random seed release caused by plant responses to weather conditions is important for seed dispersal. Much is known about the effects of wind speed and turbulence, but our understanding of the effects of water loss on seed release is either qualitative, or indirect and phenomenological.
Aims : To quantify the empirical relationship between water loss and seed release.
Methods : Capitula of the invasive thistles Carduus acanthoides and C. nutans were collected from the field and treated for either 0, 1 or 2 days in the laboratory at three different vapour pressure deficit levels (3.4, 9.5 and 17.0 hPa) to cause a range of water loss values. Total seed release was quantified before and during wind tunnel trials.
Results : Water loss was the only significant predictor of whether or not capitula released any seeds. The number of seeds released was predicted by water loss, capitulum diameter and herbivore damage, with the same amount of water loss having less effect on larger capitula.
Conclusions : These results represent an important step towards using weather data to predict seed release for many xerochastic species. Incorporating the effects of water loss on seed release into mechanistic seed dispersal models will greatly improve predictions of when and how far seeds disperse.
Acknowledgements
This research was funded by the National Science Foundation (grants DEB-0315860 and DEB-0614065 awarded to KS). In particular, thanks to the NSF REU programme for funding KMM. Financial support from the Netherlands Organisation for Scientific Research (NWO-grant 863.08.006) is acknowledged by EJ. Thanks also to the Penn State Department of Aerospace Engineering for allowing us to use their wind tunnel. Brian Tom, Julio Gomez, Thomas Bibby, Lidewij Keser, Amy Leib, Carwyn Sposit, Caitlin Sullivan, Matthew Jennis, Stephanie Freed, Jordyn Rivell, Catherine Cruz-Ortiz, Richard Ashby, Brian Butala, Rick Pongrance, Chelsea Sutherland, Maggie Wilkens, Emily Haner, Brosi Bradley, Megan Lundgren, Mason Heberling, Jennifer Stella, Leah Ruth and Peter Marchetto provided field and lab assistance. Suann Yang, David Mortensen and Scott Isard provided many helpful comments on this manuscript.