Growth and physiology responses of Phragmites australis to combined drought-flooding condition in inland saline-alkaline marsh, Northeast China

As a special ecosystem in western Songnen Plain, Northeast China, Phragmites australis saline-alkaline marsh degrade to saline meadow or even alkaline spots progressively, due to the interruption of the water supply. It was the basis to restore the saline-alkaline marsh successfully, that understanding the responses of P. australis to flooding in dried saline-alkaline marsh. Pot experiments were conducted to explore an optimum flooding time for restoring inland saline-alkaline marshes by determining the changes in the growth and physiology of P. australis in response to five different combined drought-flooding treatments (DF04, DF13, DF22, DF31 and DF40). The results showed that the long-term flooding without drought condition (DF04) was not the most favorable condition for the largest effective accumulation of plants biomass, although it gave rise to the highest population height. The combined drought-flooding treatment that drought in one month and flooding in subsequent three months (DF13) was proved as the optimum flooding time, not only obtaining the largest biomass, but also effectively reducing the sodium ion absorbed by plant shoots. Subsequently, the accumulation of sodium ion in plant shoots increased significantly with the delay of flooding from DF22 to DF40 treatments, and the significant enhanced photosynthetic activity implied the evident physiological responses to drought stress.