A comparative study of morphology and growth traits between Phragmites australis and Imperata cylindrica under varying ground water table in the coastal wetland of Yangtze River Estuary

Abstract

Phragmites australis is a constructive species in the tidal wetland in the Yangtze Estuary of China. Imperata cylindrica, a typical perennial mesophyte, is currently spreading wetlands previously dominated by the reed population and changing the structure and function of native ecosystem. Soil ground water table could affect soil physical, chemical and biogeochemical characters, which in turn influence the morphology and growth of P. australis and I. cylindrica. How to control the spread of I. cylindrica and maintain native community becomes one of the key problems for the wetland management. The relationship between the morphology and growth of P. australis and I. cylindrica and ground water table was investigated by using one-way ANOVA and Pearson correlative analysis in order to find how reed and Cogongrass respond to changes of ground water table in coastal wetland at the shoot level and at the population level. The investigation found that the rise of ground water table improved the population density but no otherwise obvious effects P. australis seedlings. The population density of I. cylindrica seedlings decreased with the rise of ground water table. At the shoot level, plant height, stem diameter, leaf area, aboveground biomass and relative growth rates of P. australis were significantly higher at middle water table than at low and high water tables. Besides plant height and base diameter, other morphological and growth traits of I. cylindrica showed no significant differences at the three ground water tables. At the population level, the population density, leaf area index, leaf biomass, stem biomass and aboveground biomass of P. australis increased with the ground water table, while those of I. cylindrica decreased. Although the growth of I. cylindrica was worse than P. australis at the shoot level, I. cylindrica spread rapidly throughout the reed population by strong agamogenesis ability, especially at low ground water table. Therefore a higher wetland ground water table at the early stage of the growing season may inhibit the growth of mesophyte I. cylindrica, and benefit the restoration of structure and function of P. australis-dominated wetland community.