Role of stele and cortex in understanding and predicting root tensile properties.

BACKGROUND AND AIMS

The mechanical properties of plant roots are crucial for soil stabilization and vegetation restoration. To effectively employ bioengineering methods, understanding the tensile properties of plant roots is essential. In most studies, root diameter is used as predictor of tensile strength but this fails to accurately describe root mechanical behavior. The stele and cortex, as two anatomical parts of root, their actual mechanical behavior and specific contributions to root biomechanisms remain unclear.

METHODS

Tensile tests and scanning electron micrography (SEM) were performed on roots of four typical species (Robinia pseudoacacia, Pinus tabuliformis, Vitex negundo and Syzygium aromaticum) in Loess Plateau of China to investigate the roles of stele and cortex in explaining the tensile strength. Then, based on the "same strain" principle, a tensile strength prediction model was developed and validated by plant root.

KEY RESULTS

The stele and cortex of roots exhibited distinct mechanical behaviors: elastic-plasticity and linear elasticity, respectively. The tensile strength was negatively correlated with diameter increasing, the stelar diameter and cortical thickness were positive correlated with diameter increased. The cortex had lower tensile strength, strain at maximum stress, and thickness compared to the stele. The observed increase in scatter of tensile strength with decreasing root diameter was attributed to the higher coefficient of variation (CV) in cortical tensile strength compared to the stele. Notably, predicted results of intact root tensile strength fell within the 95% prediction interval (PI) of the measured intact root tensile strength and could be enhanced about 30% to 80% by strengthening dataset quality.

CONCLUSIONS

Our results demonstrated the actual mechanical behavior characteristics of cortex and stele, and a new perspective for addressing the mechanical properties of roots using composite materials mechanics. The findings of this study will provide a theoretical foundation for implementing plant-based ecological restoration and disaster prevention measures.