Response of tensile properties in Cynodon dactylon root to submersion duration

Abstract: Plants can significantly alter the physiological and ecological characteristics to adapt to the continuous submersion in the water-level fluctuation zone, thus leading to the performance of root on soil reinforcement. However, it is still unclear on the effects of submersion duration on the tensile properties of plant roots. In this study, the dominant plant in the water-level fluctuation zone of the Three Gorges reservoir area, Cynodon dactylon, was selected as the research object. The seeds were sown at 15 g/m2 on a purple soil field in August 2019, and the maintenance was then conducted more than two years before the beginning of the submersion test. Samples were taken in September 2021 and then submersed in the water tank with a submerged depth of 50 cm. Among them, the water tank was covered with the black cloth to simulate the dark condition during submersion. The unsubmerged condition was used as the control. The root weight density, root activity, and tensile properties were analyzed under eight submersion durations (0, 15, 30, 60, 90, 120, 150, and 180 d), in order to evaluate the response of tensile properties of Cynodon dactylon root to submersion duration. The results indicated that there was a rapid decrease in the root weight density and root activity, followed by a slow but continuous decline with the increasing of submersion duration in the submersion group, compared with the control. The root weight density and root activity decreased by 28.42%, and 55.80%, respectively, for the submersion duration 180 d, compared with at the beginning of the submersion test. The root weight density and root activity decrease in the initial stage of submersion (15 d), accounting for 65.15% and 75.86% of the total decrement, respectively. Meanwhile, the maximum tensile strength of the root was closely related to the root diameter with the power function. The tensile force and tensile strength coefficient a, c decreased with the increase of submersion duration, while the tensile force and tensile strength power coefficient b, d showed no outstanding change. The tensile force and tensile strength coefficient a, c for the relation of root diameter with the maximum tensile strength and tensile strength decreased by 38.42%, 42.86%, 58.27%, 52.48%, 55.95%, 57.03%, 59.46%, and 38.45%, 42.87%, 58.26%, 52.50%, 55.95%, 55.95%, and 59.48%, respectively for the submersion duration15, 30, 60, 90, 120, 150, and 180 d, compared with at the beginning of the submersion test. The initial stage of submersion accounted for 64.61% and 64.64% of the total decrement of fitting tensile force and tensile strength coefficient a, and c, respectively. The response degree of root tensile properties to the submersion also varied with the root diameter. Specifically, the decrement of the maximum tensile strength increased with the increase of root diameter, while the decrement of tensile strength increased with the decrease of root diameter. Moreover, the tensile force and tensile strength coefficient a, c for the relation of root diameter with the maximum tensile strength and tensile strength shared a significant logarithmic relationship with the root activity. Therefore, the submersion environment significantly reduced the root weight density, root activity, and tensile properties. The root activity can be expected to better explain the changes in the tensile properties. The finding can be of great significance to explore the plant root on soil reinforcement under a submersion environment in the water-level fluctuation zone.