Abstract
Root mechanical traits, including tensile strength (Tr), tensile strain (εr), modulus of elasticity (Er) and tensile toughness (Wr), play a key role in plant functioning (e.g., anchorage and stem stability). Yet, their variability and their relationships with other root traits are poorly known. Here, we characterize Tr, εr, Er and Wr at both intra-and interspecific levels and examine how they covary with other root traits related to root economics space (RES). We used twelve herbaceous species from contrasting taxonomical families grown in controlled plein-air conditions. For each species, we excavated root systems and measured morphological and chemical traits and mechanical traits at two locations (proximal versus distal) for two root types (absorptive versus transport roots). Transport roots tended to show higher mechanical trait values than absorptive roots, especially for εr, while the location where the root was sampled showed a limited effect on root mechanics. The five monocots (Poaceae species) had higher mechanical traits than the seven dicots (including five Fabaceae species) except for Er. Root mechanical traits covaried positively and were strongly positively correlated with specific root length, i.e., a trait related to soil exploration strategy, and negatively with root diameter and root tissue density, i.e. a trait related to root life span. We demonstrate the important role of species category and root type in governing mechanical trait variation at both intra-and inter-specific levels. Our results can be regarded as the first evidence of the link between root mechanical robustness and the RES through a strong association with the 'do-it-yourself' soil exploration strategy.