The strength of plants: theory and experimental methods to measure the mechanical properties of stems

Abstract

From the stems of agricultural crops to the structural trunks of trees, studying the mechanical behaviour of plant stems is critical for both commerce and science. Plant scientists are also increasingly relying on mechanical test data for plant phenotyping. Yet there are neither standardized methods nor systematic reviews of current methods for the testing of herbaceous stems. We discuss the architecture of plant stems and highlight important micro- and macrostructural parameters that need to be controlled and accounted for when designing test methodologies, or that need to be understood in order to explain observed mechanical behaviour. Then, we critically evaluate various methods to test structural properties of stems, including flexural bending (two-, three-, and four-point bending) and axial loading (tensile, compressive, and buckling) tests. Recommendations are made on best practices. This review is relevant to fundamental studies exploring plant biomechanics, mechanical phenotyping of plants, and the determinants of mechanical properties in cell walls, as well as to application-focused studies, such as in agro-breeding and forest management projects, aiming to understand deformation processes of stem structures. The methods explored here can also be extended to other elongated, rod-shaped organs (e.g. petioles, midribs, and even roots).

Mechanical stimulation in Brachypodium distachyon: Implications for fitness, productivity, and cell wall properties

“…Although the treatment responses in terms of many of the macroscopic and biochemical traits tended to be similar between the two accessions, a notable exception were those involving the vascular system. Mechanical stimulation affects architectural and anatomical features in dicot stems (Paul‐Victor & Rowe, ; Rigo, ; Roignant et al, ), which may influence their mechanical properties (Shah, Reynolds, & Ramage, ). Mechanical stimulation has been reported to increase xylem tissue in a range of dicots (Hepworth & Vincent, ; Hunt & Jaffe, ; Jaffe, , ), but the situation in rice may be more complex.…”

Brassinosteroids Influence Arabidopsis Hypocotyl Graviresponses Through Changes In Mannans And Cellulose

“…The two prerequisites for normal negative gravitropism in young shoots, mechanical 398 strength and gravitropic bending, are based on distinct physiological mechanisms, which 399 are linked through the cell wall characteristics. The mechanical strength of young shoots is 400 defined by turgor and their primary cell walls (Shah et al, 2017). This is well illustrated by 401 wilting, a loss of turgor, when young shoots do not keep their upright position and lie down 402 on the ground.…”

The genetic architecture of biomechanical traits in sorghum

“…The E is reported (MPa). In the context of this study, E is a measure of the ability of a material or composite material to resist mechanical stress (Niklas, 1992;Shah et al, 2017), henceforth referred to as "stiffness." In this study, stalk strength is defined as the maximum stress required to break the structural integrity of a stem or internode under a bending load (Niklas, 1992).…”

“…Breeding crops to resist wind‐induced stem lodging is crucial for food security and bioenergy sustainability. Stem lodging is defined as an irreversible mechanical stem failure at both the microstructure and macrostructure scales (Shah, Reynolds, & Ramage, 2017). Stem failure results from the application of excessive bending forces at the basal internodes, which is determined primarily by the interaction of wind‐derived force and stem morphology, anatomy, and bulk tissue mechanical properties.…”