## 5 Conclusions  
Short-term flooding promotes further growth of the plant root system, as evidenced by increases in root length, surface area, volume, and diameter. However, as the duration of flooding increased, the growth rate of the root system gradually slowed and eventually exhibited a decreasing trend with an increasing magnitude. As the duration of flooding increases, the proportion of _Carex_ roots with a diameter greater than 0.5 cm initially decreases before subsequently increasing. _Cynodon_ demonstrates a trend of first increasing and then decreasing, _Eleusine_ also exhibits a pattern of initial decrease followed by an increase after reaching a peak in the early stages. These three plant species reached their extremes at 180 days, 90 days, and 30 days, respectively. These three plant species exhibited significant negative correlations between root diameter and tensile strength under flooding conditions, but displayed distinctly species-specific patterns in their elastic modulus responses. The maximum tensile force and elastic modulus generally declined as flooding duration increased, while tensile strength initially increased before subsequently decreasing. Regarding the maximum tensile force, _Carex_ and _Cynodon_ both reached their optimal values at 90 days of flooding, whereas _Eleusine_ peaked earlier, at 60 days. Tensile strength values for both _Carex_ and _Cynodon_ peaked at 90 days of flooding, while the peak tensile strength of _Eleusine_ was observed under a shorter flooding duration (<60 days). These results highlight notable interspecific differences in root mechanical adaptability in response to prolonged flooding stress. The root-soil composite shear strength of _Carex_ exhibited an initial increasing trend during the early flooding stage but gradually decreased after 120 days. For _Cynodon_, shear strength consistently showed a stable and gradual decline throughout the entire flooding period. In contrast, _Eleusine_ experienced a rapid reduction in shear strength shortly after flooding began (30 days), approaching levels comparable to the unvegetated control after 180 days. Both _Carex_ and _Cynodon_ maintained relatively high shear strengths even after prolonged flooding, whereas _Eleusine_ demonstrated significant sensitivity and vulnerability under extended flooding stress. Clear interspecific differences were observed among the three plant species regarding their responses of root-soil composite shear strength, internal friction angle, and cohesion to prolonged flooding stress. In the simulated flooding environment of the Yangtze River Basin, the root-soil composite shear strength of _Carex_ exhibited an initial increasing trend during the early flooding stage but gradually decreasedafter 120 days. For _Cynodon_, shear strength consistently showed a stable and gradual decline throughout the entire flooding period. In contrast, _Eleusine_ experienced a rapid reduction in shear strength shortly after flooding began (30 days), approaching levels comparable to the unvegetated control after 180 days. Both _Carex_ and _Cynodon_ maintained relatively high shear strengths even after prolonged flooding, whereas _Eleusine_ demonstrated significant sensitivity and vulnerability under extended flooding stress. _Carex_ is optimally applied in the restoration and protection of areas subjected to three to four months of flooding, with its ornamental value being particularly pronounced. _Cynodon_ performs best in areas with up to six months of flooding, _Eleusine_ is especially effective in regions with less than two months of flooding.