Climate‐Dependent Heat‐Triggered Opening Mechanism of Banksia Seed Pods

• Published in: Advanced science Vol. 5; no. 1; pp. 1700572 - n/a
• Main Authors: Huss, Jessica C., Schoeppler, Vanessa, Merritt, David J., Best, Christine, Maire, Eric, Adrien, Jérôme, Spaeker, Oliver, Janssen, Nils, Gladisch, Johannes, Gierlinger, Notburga, Miller, Ben P., Fratzl, Peter, Eder, Michaela
• Format: Journal Article
• Language: English
• Published: Germany Wiley Open Access 01-01-2018; John Wiley and Sons Inc
• Subjects: banksia; Biomimetics; dimensional stability; Engineering Sciences; Environmental conditions; Environmental gradient; fire; Fire prone ecosystems; Fires; Fruits; Irreversible deformation; Material characteristics; Materials; Temperature dependent; triggered follicle opening; fire; banksia; triggered follicle opening; dimensional stability
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.201700572

Heat‐triggered fruit opening and delayed release of mature seeds are widespread among plants in fire‐prone ecosystems. Here, the material characteristics of the seed‐containing follicles of Banksia attenuata (Proteaceae), which open in response to heat frequently caused by fire, are investigated. Material analysis reveals that long‐term dimensional stability and opening temperatures of follicles collected across an environmental gradient increase as habitats become drier, hotter, and more fire prone. A gradual increase in the biaxial curvature of the hygroscopic valves provides the follicles in the driest region with the highest flexural rigidity. The irreversible deformation of the valves for opening is enabled via a temperature‐dependent reduction of the elastic modulus of the innermost tissue layer, which then allows releasing the stresses previously generated by shrinkage of the fiber bundles in the adjacent layer during follicle drying. These findings illustrate the level of sophistication by which this species optimizes its fruit opening mechanism over a large distribution range with varying environmental conditions, and may not only have great relevance for developing biomimetic actuators, but also for elucidating the species' capacity to cope with climatic changes.
Seed pods of Banksia attenuata open through cycles of humidity following an initial heat stimulus. The heat‐triggered, initial opening process is regulated by an interplay of geometry, temperature, and mechanics. Gradual changes in curvature result in distinct opening temperatures along a pronounced climatic gradient in Western Australia with varying fire risk.