How does root biodegradation after plant felling change root reinforcement to soil?

Abstract

Previous studies have shown that root reinforcement provided by trees could decrease over time after stem cutting. The short-term changes in root mechanical and structural traits associated with root reinforcement after stem cutting have not been fully studied. We aimed to quantify the temporal changes in root mechanical and structural traits following stem cutting, and to identify the major drivers of root reinforcement deterioration. At six elapsed times (zero, one, three, six, nine, and twelve months) after stem cutting of the species Symplocos setchuensis Brand, we measured shear strength for both rooted and root free soils, root failure modes, root mechanical traits (tensile strength, Young’s modulus, and tensile strain) and structural traits (cellulose, hemicellulose and lignin contents). Both root mechanical and structural traits significantly differed as a function of root diameter and time after stem cutting. Tensile strength decreased 19.7% while Young’s modulus decreased 46.9% twelve months after stem cutting. Hemicellulose content showed the greatest decrease (45.3%) among the structural traits. The relative reduction in magnitude was higher for fine roots than coarse roots. Additional shear strength (at the yield point) provide by roots decreased 85.9% twelve months after stem cutting. Our findings demonstrate a higher rate of root reinforcement deterioration after stem cutting than previously reported in literatures. Our results suggest that the underlying mechanism of deterioration of root reinforcement is more likely caused by a shift of root failure from tensile breakage to slide-out failure, and a decline in root Young’s modulus.