Summer dormancy in an endangered riparian shrub Myricaria laxiflora: Changes in branches, leaves, and nonstructural carbohydrates

Myricaria laxiflora is a rare and endangered shrub that is distributed in the floodplain of the Yangtze River’s mainstream. The plants experience long-lasting flooding stress during the summer every year. The aboveground portion of the M. laxiflora plants exhibits yellowing and withering before summer flooding. Five quadrats were established in the habitat of remnant M. laxiflora populations. The variation of environmental factors in the habitat was investigated. Changes in the branches, leaves, and nonstructural carbohydrates were quantified before summer flooding by randomly selecting plants from the quadrats to reveal whether M. laxiflora goes into dormancy and adapts to the upcoming flooding by dormancy. The results showed that the number of branches and leaves gradually decreased with the approach of summer flooding. In the branches and leaves, the nonstructural carbohydrates, total soluble sugar, fructose, and starch contents decreased continuously. However, the content of sucrose first increased, then decreased. Pearson correlation and stepwise regression analyses showed that changes in the characteristics of branches and leaves and the content of nonstructural carbohydrates all exhibited significant correlation with daylength. However, there was no significant correlation with daily average temperature, underground water level, or soil water content. Considering the changing pattern of branches and leaves these result, along with the simultaneous decrease in the content of nonstructural carbohydrates, it could be deduced that dormancy existed in the remnant populations of M. laxiflora before summer flooding; the plants adapted to the approaching summer flooding stress via endodormancy. The main environmental factor that induced dormancy in this species was daylength.