Impact of regulated water level fluctuations on the sexual reproduction of remnant Myricaria laxiflora populations

Abstract

The construction and operation of the Three Gorges-Gezhou cascade water conservancy and hydropower projects has dramatically changed downstream water level fluctuations. Remnant populations of Myricaria laxiflora, an aquatic endangered plant, have been severely affected by the regulated water level fluctuations. In this study, the impact of regulated water level fluctuations on sexual reproduction of M. laxiflora were assessed by investigating variations in the number of flowering branches, inflorescences, flowers, and fruits, seed vigor, and 1,000-seed weight of remnant M. laxiflora populations across a water level fluctuation gradient. Our findings indicate that the water level fluctuation gradient significantly influences the sexual reproduction of M. laxiflora. The flowering and fruit setting of M. laxiflora plants in the upper region of the habitat were superior to those in the middle and lower regions. The mean flowering branches, the number of inflorescences per branch, and the number of flowers of M. laxiflora plants in the upper region of the gradient were 150.0%, 356.7%, and 196.8% higher than those in the middle region, and 124.7%, 491.7%, and 173.6% higher than those in the lower region, respectively. The number and rate of fruit settings of M. laxiflora plants in the upper region of the gradient were 389.1% and 61.1% higher than those in the middle region, and 788.4% and 192.6% of those in the lower region, respectively. The number of seeds per fruit, 1,000-seed weight, and seed vigor of the M. laxiflora plants in the upper region of the gradient were 7.3%, 36.2%, and 181.6% higher than those in the middle region, and 10.9%, 31.6%, and 176.1% higher than those in the lower region, respectively. Further analysis indicated that flowering, fruit setting, and seed development of M. laxiflora were correlated with soil water content and duration of habitat exposure, which are aquatic ecological environmental factors that are related to water level fluctuations. Taken together, the findings of this study indicate that water level fluctuations regulated by the operation of the cascade water conservancy and hydropower projects affect the sexual reproduction of remnant Myricaria laxiflora populations. Keywords: Endangered species, Myricaria laxiflora, Riparian zone, Flowering and fruit setting, Aquatic ecological environment