Failure without tears: Two-step attachment in a climbing cactus Article Swipe
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· 2023
· Open Access
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· DOI: https://doi.org/10.5281/zenodo.7868179
· OA: W4393700625
Climbing plants can be extremely adaptable to diverse habitats and capable of colonizing perturbed, unstructured and even moving environments. The timing of the attachment process, whether instantaneous (e.g., a pre-formed hook) or slow (growth process) crucially depends on the environmental context and the evolutionary history of the group concerned. We observed how spines and adhesive roots develop and tested their mechanical strength in the climbing cactus <em>Selenicereus setaceus</em> (Cactaceae) in its natural habitat. Spines are formed on the edges of the triangular cross section of the climbing stem and originate in soft axillary buds (areoles). Roots are formed in the inner hard core of the stem (wood cylinder) and grow via tunnelling through soft tissue, emerging from the outer skin. We measured maximal spine strength and root strength via simple tensile tests using a field measuring Instron device. Spine and root strengths differ, and this has a biological significance for the support of the stem. Our measurements indicate that the measured mean strength of a single spine could theoretically support an average force of 2.8 N. This corresponds to an equivalent stem length of 2.62 m (mass of 285 g). The measured mean strength of root could theoretically support an average of 13.71 N. This corresponds to a stem length of 12.91 m (mass of 1398 g). We introduce the notion of two-step attachment in climbing plants. In this cactus, the first step deploys hooks to attach to a substrate; this process is instantaneous and is highly adapted for moving environments. The second step involves root growth for more solid attachment to the substrate; this process involves “slow” root growth and adhesion. The advantage of the two-step strategy is that fast hook attachment can steady the plant for the slower root attachment. This strategy is effective in highly variable and heterogeneous environments when climbing plants are faced with constant moving and perturbed environmental conditions in many ecosystems. We discuss how two-step mechanisms are of interest for technical anchoring applications particularly for “soft-bodied” artefacts, which have to deploy hard and stiff materials originating from a soft compliant body and where tasks involving attachment take place in highly unstable and unpredictable environments.
