## 3 Results  
### Relationship between Root Morphological Indexes and Elevation of Cynodon dactylon Roots  
Morphological indicators of plant roots, such as root length, root diameter, root surface area, and root volume, directly influence the plant's ability to absorb soil nutrients and water, as well as to anchor the soil. To investigate the effect of elevation on the growth of _Cynodon dactylon_, this paper analyzed the root scanning data of _Cynodon dactylon_ at different elevations (low, medium, and high) in the Ertan and Guanyinyan reservoirs. The analysis results showed that the root length, surface area, average diameter, and total root volume of _Cynodon dactylon_ exhibited a certain range of variation under different elevation conditions (Figure 2). Specifically, the root length varied from 17.1920 to 28.0508 cm, the surface area varied from 1.9814 to 4.1623 cm\({}^{2}\), the mean diameter varied from 0.3607 mm to 0.4898 mm, and the total root volume varied from 0.0212 to 0.0508 cm\({}^{3}\). Under all elevation conditions, _Cynodon dactylon_ located at Ertan Reservoir elevation (H) exhibited the highest root characterization index. Specifically, its root length was 28.0508 cm, the root surface area was 4.1623 cm\({}^{2}\), the average diameter was 0.4898 mm, and the total root volume was 0.0508 cm\({}^{3}\). Compared to low elevations (L and M), the root length increased by 57.3% and 21.47%, the root diameter increased by 24.85% and 13.92%, the root surface area increased by 93.5% and 67.37%, and the total root volume increased by 119.91% and 107.36%, respectively. This result indicates that elevation had a significant effect on the plant root characteristics of _Cynodon dactylon_. In addition, the pattern of changes in the root characteristics of _Cynodon dactylon_ with elevation in the Guanyinyan Reservoir was consistent with that of the Ertan Reservoir. However, compared with the Ertan Reservoir, the length, diameter, surface area, and total volume of the _Cynodon dactylon_ system in the Guanyinyan Reservoir area decreased by 4.38%, 5.99%, 6.43%, and 6.65%, respectively. This result suggests that the environmental conditions of different reservoirs affect the plant root characteristics of _Cynodon dactylon_. Based on previous studies on plant roots in the riparian zone [11], this paper conducts a detailed hierarchical analysis of plant roots at different gradients. It classifies the root diameters into four grades and performs an in-depth study of the length, surface area, and volume of each grade. The detailed data are shown in Figures 3 and 4. It is evident from Figures 3 and 4 that the _Cynodon dactylon_ in Ertan Reservoir and Guanyinyan Reservoir both exhibited a higher percentage of plant roots with diameters exceeding 0.4 mm across various elevation gradients. Among them, the percentage of water storage in the Ertan Reservoir ranged from 42.85% to 100%, while that of the Guanyinyan Reservoir ranged from 30.71% to 100%. This indicates that the diameter of the mature _Cynodon dactylon_ system is generally larger than 0.4 mm. The length, surface area, and volume of _Cynodon dactylon_ system with rhizomes ranging from 0-0.4 mm accounted for 0% in both reservoirs under the H gradient. This indicates that under the higher elevation gradient, the root growth of _Cynodon dactylon_ was mainly concentrated in the larger-diameter part. Under the L and M gradients, the length, surface area, and volume of the _Cynodon dactylon_ system in Guanyinyan Reservoir were greater than the corresponding morphological indicators in Ertan Reservoir. In the range of 0.4 to 0.5 mm of rhizomes, the difference between the two reservoirs under the low (L) gradient was not significant. However, under the medium (M) and high (H) gradients, the proportion of the _Cynodon dactylon_ system in Guanyanyan Reservoir was considerably greater than that in Ertan Reservoir.