## 4 Discussion
### Effect of Elevation on Mechanical Properties of Plant Root  
The diameter is one of the most significant factors influencing the mechanical properties of plant roots [9; 10; 11; 21]. There is an evident size effect on both the single-root tensile force and single-root tensile strength concerning root diameter. The single-root tensile force increases with root diameter, while the single-root tensile strength decreases. The relationship between these two root indexes and root diameter can be modeled by a power function, aligning with findings from other studies. In this experiment, the average diameter and total root volume of _Cymodon dactylon_ roots increased with a higher elevation and a shorter flooding time. This implies that the maximum tensile strength will increase with elevation, and the ultimate tensile strength will also increase with elevation. Both strengths will be correlated with the diameter in a power function. This result is consistent with the findings of numerous national and international studies on the root systems of herbs, shrubs, and other plants [13; 21; 22; 23; 24]. [PERSON] et al., 2005 [25] concluded that the fiber content within the plant root is closely related to the root diameter and tensile strength, which are functions of the root diameter. The internal morphology of the plant root is a complex laminar structure composed of cells whose microstructure and chemical composition (e.g., cellulose, hemicellulose, and lignin) synergistically affect the tensile mechanical properties [26]. The elongation and modulus of elasticity of _Cymodon dactylon_ decreased as a power function with the increasing root diameter, which is consistent with the findings of [PERSON] et al., 2023 [27]. As the root diameter increases, the cellulose and hemicellulose content within the plant root also increase, leading to a decrease in the ultimate elongation and modulus of elasticity of the plant root. The maximum tensile force, ultimate tensile strength, and Young's modulus of _Cymodon dactylon_ increase with elevation, while the ultimate elongation decreases with elevation. The extreme hydrological conditions in large reservoirs, characterized by long-term flooding exposure-flooding alternation, have a significant impact on the plant biology in the floodplain. This variation also results in differences in the physicochemical properties and water content of the soil across various elevation gradients, as well as during different degrees of dry and wet cycles. These changes in soil properties and the surrounding conditions alter the tissue composition of the _Cymodon dactylon_ system, ultimately leading to variations in elevation. The microstructure and chemical composition of individual roots of the same species vary across different elevation gradients. These differences are the primary factors contributing to the significant variations in tensile strength characteristics observed in individual roots of _Cymodon dactylon_ across different elevation gradients [13; 28]. Flooding affects the maximum tensile strength of plant roots primarily by altering root vigor, and this impact is most pronounced at the onset of flooding [18]. Roots with high vigor have high maximum tensile strength, while those with low vigor have low maximum tensile strength. Flooding causes _Cymodon dactylon_ roots to undergo a large amount of anaerobic respiration. The ethanol produced is somewhat toxic to the _Cymodon dactylon_ roots themselves, which reduces root vigor, leading to a significant reduction in the maximum tensile strength of _Cymodon dactylon_ roots [18]. [PERSON] [29] and some other scholars believe that the mechanical properties of plant roots are closely related to the cellulose, hemicellulose, and lignin present inside the roots. Lignin, etc., and different elevation gradients would lead to varying plant growth, as well as different cellulose, hemicellulose, and lignin content.