## 4 Discussion
### Root Diameter and Varying Flooding Durations Affect Root Strength  
The results of the root mechanics experiments indicate that variations in flooding duration lead to significant differences in the fitting equations between the root diameter and root mechanical properties. This may be attributed to the distinct ways in which the root diameter and root mechanical properties influence mechanical characteristics, as well as the differing overall impacts of the two on various mechanical indicators. However, the influence on diameter is not uniformly advantageous. Following exposure to a flooding environment, the root strength of sedge significantly decreased, while that of bermudagrass increased. The flooding environment directly influences the strength of the relationship between the root diameter and the mechanical properties of the root system. For _Carex_, this significance gradually diminishes with an increase in flooding duration. In contrast, both _Cynodon_ and _Eleusine_ exhibit a trend that initially increases before subsequently decreasing. Plant root systems exhibit distinct behaviors in soil environments with varying water contents, and there is a correlation between the amount of water lost by the root system and the increase in root strength relative to root diameter [30]. One factor contributing to the high variability in the strength of small-diameter root systems is the water status of the root system, which may be influenced by the relatively large evaporative surface area associated with relatively small root diameters [31]. Under prolonged flooding, the tensile strength of the large-diameter root system of _Carex_ gradually decreased, in the context of roots with a small diameter it is interesting the fact that at the smallest root diameters, grass roots have the highest tensile strength and shrubs the lowest [32]. The tensile strengths of grass and tree species tend to converge at root diameters above 5 mm. In contrast, _Cynodon_ initially strengthened the large-diameter root system during the first 60 days of flooding before shifting its focus to enhance the small-diameter root system. _Eleusine_ achieved optimal root system tensile strength after 60 days of flooding, particularly in the medium-diameter root system, which has a diameter range of 0.3-0.6 cm. The changes in root system elongation of _Carex_ and _Cynodon_ under flooding were more complex, with different species and varying flooding conditions leading to distinct responses for each [33; 34]. Different durations of flooding significantly affected the variation in single root elongation in _Eleusine_. The results indicated that _Eleusine_ was able to rapidly increase root elongation during the initial flooding period to penetrate deeper into the soil. However, over time, its root system may have undergone lignification, resulting in a significant decrease in elongation and loss of activity after 120 days of flooding. In the context of lignification, lignin acts as a matrix, increasing the mechanical strength of the cell wall, therefore cascading in the root systems and the soil-root interaction [35]. When combined with the study of changes in root morphology, it can be concluded that some smaller root systems with higher tensile strength may be limited by the larger root systems of the plant itself. The large-diameter roots, which were not well adapted to the flooded environment, became progressively softened by the water due to prolonged inundation, resulting in a decline in their strength. This decline may be attributed to the continuous weakening of the ability of the root system to evaporate water as the plant enters a persistently flooded environment. Additionally, gas exchange between the root system and the surrounding environment was hindered, leading to rapid oxygen consumption by both plants and microorganisms, which resulted in a hypoxic state in the root system. Under hypoxic conditions, aerobic respiration in the root system is inhibited.