Elastic property and fracture mechanics of lateral branch-branch junctions in cacti: A case study of Opuntia ficus-indica and Cylindropuntia bigelovii

Abstract

Species with various reproductive modes accompanied by different mechanical properties of their (lateral) branch-branch junctions have evolved in the cactus subfamily Opuntioideae. Older branches of Opuntia ficus-indica with fracture-resistant junctions often bear flowers and fruits for sexual reproduction, whereas younger branches break off easily and provide offshoots for vegetative propagation. Cylindropuntia bigelovii plants are known for their vegetative reproduction via easily detachable branches that can establish themselves as offshoots. We characterized the elastic and fracture behaviors of these lateral junctions by tensile testing and analyzed local strains during loading. Additionally, we carried out finite element analyses to quantify the influence of five relevant tissue layers on joint elastic behavior. Our fracture analysis revealed various fracture modes: (i) most young samples of Opuntia ficus-indica failed directly at the junction and had smooth fracture surfaces, and relative fracture strain was on median 4% of the total strain; (ii) most older samples of Opuntia ficus-indica failed at the adjacent branch and exhibited rough fracture surfaces, and relative fracture strain was on median 47%; (iii) most samples of Cylindropuntia bigelovii abscised directly at the junction and exhibited cup and cone surfaces, and relative fracture strain was on median 28%. Various geometric and mechanical properties such as junction area, fracture energy, and tensile strength were analyzed with respect to significant differences between species and age of sample. Interestingly, the abscission of lateral branches naturally triggered by wind, passing animals, or vibration showed the following differences in maximum force: 153 N (older Opuntia ficus-indica), 51 N (young Opuntia ficus-indica), and 14 N (Cylindropuntia bigelovii).

Digital image correlation techniques for motion analysis and biomechanical characterization of plants

“…For example, although a stereo camera setup can provide a 3D visualization of the surface, it is always limited to the area of the sample visible to the cameras. Part of the motion and deformation remains unresolved, providing limited information, especially for multi-material systems or very heterogeneous materials, as is often the case with plant samples ( Sachse et al., 2020 ; Durak et al., 2022b ; Mylo et al., 2022b ). One way to overcome this is to use a multi-view DIC system, where one or more (stereo) camera setups are installed around the sample to provide additional viewing angles ( Chen et al., 2013 ; Patil et al., 2017 ; Janeliukstis and Chen, 2021 ).…”

“…(C) Local strain of the three points during tensile testing, with the vertical grey line marking the strain state of (B) . (D–G) Strain analysis of branch-branch junctions in cacti under tensile loading (modified from Mylo et al., 2022b ). Strain distribution of a young junction of Opuntia ficus-indica (D) , an older junction of O. ficus-indica (E) and a junction of Cylindropuntia bigelovii (F) at about half the strain rate that led to failure.…”

Longevity of System Functions in Biology and Biomimetics: A Matter of Robustness and Resilience

“…Moreover, we find abrupt transitions leading to a spatio-temporal controlled shedding of individual plant organs (abscission), such as between branches and petioles resulting in leaf fall in autumn [ 70 , 71 ]. Another example is the chain-like arrangement of branches in certain cacti ( Opuntioideae ), in which shedding enables vegetative reproduction [ 10 , 11 , 72 ]. The concept of shedding plant organs (abscission [ 70 ] and autotomy [ 73 ]) and discarding animal appendages (autotomy [ 74 ]) is discussed as inspiration for future smart structures with controlled failures occurring in predefined positions in the structural scheme.…”

“…For individual plants, an age of up to 5000 years has thus been assigned, whereby the oldest plants are all woody conifers [ 9 ]. Special cases involve plants that reproduce asexually with clonal reproduction [ 10 , 11 ], including community-sized individuals that have a lifespan of more than 40,000 years [ 8 , 9 ] and seeds that can maintain their viability for more than 2000 years [ 12 ]. Coalified conifer cones retain their hygroscopic capacity to open and close after more than 10 million years in the ground; however, it is important to note that this is already dead tissue [ 13 ].…”

Stereo Camera Setup for 360° Digital Image Correlation to Reveal Smart Structures of Hakea Fruits

“…Its first applications were in materials science, but over the years, DIC has been utilized more and more in other research fields, such as aerospace, including large-scale composite structures [ 6 ], civil engineering, such as bridge monitoring [ 12 , 13 ], human and animal biomechanics to analyse a wide variety of organs and tissues [ 14 , 15 ] and wood research, from entire trees to processed composites [ 16 ]. In recent years, DIC has also been used in plant analysis, namely to analyse plant tissue strains under tensile loading (e.g., mistletoe–host interface [ 17 ] or the branch–branch connections of cacti [ 18 ]) to analyse compression (e.g., citrus peels [ 19 ]), and to characterise plant movements, such as the snap-buckling closure [ 20 ] and reopening [ 21 ] of the Venus flytrap or the desiccation-driven motion of pine cone scales [ 22 , 23 ]. This has led to a better understanding of the functional principles of the plant material systems, which is a prerequisite for successful transfer to bioinspired materials.…”