Attachment of vascular epiphytes through ontogeny and across taxonomic groups

• Applicant: Jessica Ying Ling Tay, Ph.D.
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541795753

It is vital for vascular epiphytes to stay permanently attached to their host plants throughout their lifetime. Propagules must obtain initial contact to the host and avoid subsequent removal. Next, secured propagules need to germinate and develop roots for attachment and lastly, growing plants must maintain their attachment despite increasing size and withstand many sources of mechanical disturbances. Though structural dependence on a host is a prominent characteristic of epiphytes, literature detailing the fundamental mechanism(s) of how they initially attach and remain attached to their hosts remains scarce. My recent publications characterised the attachment mechanism of an epiphytic orchid and aroid, and two main attachment mechanisms were identified–via adhesion and mechanical interlocking. Previous publications on epiphyte-host attachment were often linked to bark roughness. However, this connection is usually made without prior knowledge about the attachment mechanism of epiphytes to their hosts. Without this information or the relative sizes of the attaching structures, simply linking a haphazardly chosen index of bark roughness to epiphyte establishment is fundamentally flawed. An investigation of epiphyte establishment at the community level is challenging given the multitude of levels to consider, i.e., different propagule sizes, bark types, roughness, substrate angles and ontogenetic stages. Nonetheless, propagule dispersal and attachment is a good starting point for the study of the complex role of bark properties for epiphyte community assembly: unless there is vegetative propagation, failure to attach as a propagule would be an environmental filter at the local scale. In a pilot study, we investigated the effects of substrate roughness, wind speed and moisture on the retention of bromeliad seeds on the substrate. Main results showed that wind is needed for dispersal but moisture and roughed substrate can capture propagules more effectively, and that propagule structure contributes to attachment. Therefore, I aim to start a systematic investigation of epiphyte propagules to understand how the wide range of morphology relates to its attachment function. For meaningful interpretation, substrate roughness for propagule attachment will be discussed within the context of clearly defined attachment mechanism(s). Factors affecting propagule attachment will be examined, such as substrate angle and the presence of rain and wind. Lastly, though there are studies on the attachment mechanism and strength of epiphytes on different substrate roughness, the taxonomic scope is very limited–only species with velamentous roots have been studied. To investigate if there is one common attachment mechanism of epiphytes, it is important to study species with non-velamentous roots. In conclusion, this project aims to address the central question: What is the role of attachment of epiphytes through ontogeny and across different taxonomic groups?

• DFG Programme: Research Grants