Assessing biomechanical durability of alpine and subalpine leaves via measuring bend and fracture attributes

Abstract

Environmental factors, such as dynamic forces and herbivory, place pressure on plants to develop adaptive features in their leaves for resilience against external mechanical forces. Biomechanical traits enable resilience to such pressures. Biomechanical resilience is the physical robustness of a tissue, due to its structure and composition, which affords resilience to mechanical stress. Plants with a low specific leaf area (SLA) are often long-lived, and in low-nutrient environments it can cost more to replace a leaf than to protect it with biomechanical resilience. The alpine and sub-alpine environments are nutrient limited environments, which places stress on plants, limiting their growth. We hypothesised that SLA would be negatively correlated with measures of plant toughness, specifically bend and fracture moduli, in alpine and subalpine leaves. Additionally, we expected leaf thickness to be positively correlated with puncture resilience. We found no relationship between bend modulus and SLA (R² = 0.140), nor for fracture modulus and SLA (R² = 0.243). We found no relationship between leaf thickness and fracture modulus; however, the mid-vein fracture modulus was significantly higher than that of the lamina (p < 0.001), which may indicate greater resource investment into vascular tissue via constituent material toughness. Assessing leaf economic strategies of durability and longevity versus less investment and short lifespan can reveal community functional features that occur as a product of environmental pressures. Understanding plant traits that contribute to durability and, by extension, plant longevity, may help to predict how climate change will alter vegetation composition.