Root moisture content influence on root tensile tests of herbaceous plants

Root tensile strength controls root reinforcement, but a range of factors including root moisture and diameter have such a large impact that it is difficult to make predictions. In this study, we measured how variable root moisture content affects the relationship between root diameter and root tensile strength of herbaceous plants. Fresh roots of two herbaceous plants, Heteropappus altaicus and Poa sphondylodes were divided into four groups: (i) saturated in water, (ii) kept fresh, (iii) or dried for 6 h or (iv) 12 h in air. Root diameter and mechanical failure under tension before and after the moisture treatment were measured. Tensile strength and tensile force of both species decreased linearly while mean root diameter increased linearly with increasing root moisture content. Root moisture content has a large impact on the variability of root tensile strength. This emphasizes the need to avoid desiccation during testing. In field impacts of soil water potential on root strength requires further study. We recommend soaking roots in water before testing to decrease this source of error.