Potentials of mycorrhizal fungi in altering eight biomechanical properties of plant roots

Arbuscular mycorrhizal (AM) fungi are ubiquitous and impactful symbionts of most land plants and can regulate essential ecological processes. AM fungi can increase the cellulose content of root cell walls and hence the root tensile strength of grass. How AM fungi can alter other essential biomechanical properties is not clear. This study aims to study the contribution of AM fungi in altering biomechanical properties by comparing mycorrhizal and non-mycorrhizal roots. We inoculated three fungal species to vetiver grass (Chrysopogon zizanioides) for comparison. Eight root biomechanical properties (i.e., yield strain, yield stress, break strain, tensile strength, Young's modulus, plastic modulus, plastic strain, and toughness) were determined for each root using a newly developed Fortran language-based program. Inoculating AM fungi decreased both Young's modulus and plastic modulus by 23% and 17%, respectively, versus control, although it was species-dependent. Yield stress was not significantly affected, but tensile strength was increased by 7%-17% upon fungal symbiosis. Together with the increases in break strain by 15%-20%, mycorrhizal roots possessed a notably higher toughness than non-mycorrhizal roots by up to 36%. Greater root cohesion of mycorrhizal roots confirmed the enhanced (1.5-fold) factor of safety in the soil-root system. Our findings imply that AM fungi are of significant interest in plant biomechanics and geotechnical engineering. Applying AM fungi on soil slopes has considerable potential to improve vegetation and stability of green slopes.