Drying of fibrous roots strengthens the negative power relation between biomechanical properties and diameter

Aims: Test the effects of root drying on biomechanical properties of fibrous roots. 

Methods: Tensile strength and Young’s modulus of Festuca arundinacea roots were tested after full hydration and during progressive drying. Root diameter, water loss, and water content were measured for all treatments. 

Results: Hydrated roots showed weak relations between biomechanical properties and diameter. After only 30 min air-drying, both tensile strength and Young’s modulus increased significantly in thin roots (< 1 mm) and after 60 min drying, both strength and Young’s modulus showed a negative power relation with root diameter. The maximum strength and Young’s modulus values recorded after 60 min drying were respectively three- and four-times greater than in hydrated roots. Strength and Young’s modulus increased rapidly when water content dropped below 0.70 g g⁻¹. These biomechanical changes were the result of root diameter shrinkage of up to 50% after 60 min drying, driven by water loss of up to 0.7 g g⁻¹. 

Conclusions: Strength and Young’s modulus largely increased with root drying. We suggest controlling root moisture and testing fully hydrated roots as standard protocol, given that slope instability is generally caused by heavy rainfall events and loss of matric suction.