Even though rain occurs frequently in many ecosystems, the response of leaves to drop impacts remains poorly understood. Their various shapes, materials and surface features determine distinctive raindrop responses across species. In this thesis I studied the detailed kinematics and biomechanical underpinnings of drop impact responses comparing generalist photosynthetic leaves to specialised leaves of carnivorous Nepenthes gracilis plants. In Part I, I investigated the general drop leaf interaction by adapting a standard laboratory setup for biomechanical video analysis to perform high precision experiments in the field. With this setup, I tested rain drop impacts on 50 dicotyledonous leaves. I observed bending along the leaf length and twisting across the lamina in all apart from three leaves, which showed a multi-frequency bending. Superimposed, individual parts of the leaves bent at higher frequencies or the whole leaf bent at higher deformation modes. A modified bending beam model explained the bending frequency dependent on the length across all leaves independent of their geometry, material or hydrophobicity. In Part II, I investigated how the N. gracilis pitcher is adapted to exploit the impact energy of rain drops to trap prey. To localise the deformation during an impact response, I repeatedly imaged the same pitcher in a µ-CT scanner while manipulating its lid position. This revealed two distinct areas of deformation: (1) the lid-pitcher junction and (2) a section of the dorsal ’backbone’ of the pitcher. Repeating this experiment with a 3D printed replica revealed that the geometry of the pitcher, without specialised material adaptations, could explain the observed deformation. While generalist and specialist leaves showed bending responses, N. gracilis traps maximised the drop energy transfer into this specific movement minimising dissipation through other modes. Spatially separating photosynthesis and trapping function reduced the demands on the pitcher and facilitated this specialisation.
Adaptations of plant leaves for dissipating or exploiting impact energy from rain drops
Lenz, A. S. (Author). 1 Oct 2024
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)