Effects Of Gradient Waterlogging On The Control Of An Invasive Plant Spartina Alterniflora

Estuarine and coastal habitats are undergoing modification as a result of human activities.Biological invasion by species introduced by humans is one of the most serious environmental problems that may influence future economical and social development.Spartina alterniflora(smooth cordgrass),native to the Atlantic and Gulf coasts of North American,is a perennial and deep-rooted salt marsh grass.The invasive species was first introduced in 1995.With its strong adaptability and ability of diffusivity,it expanded rapidly and has formed the mono-dominant community at Chongming Dongtan Nature Reserve,Shanghai.Chongrning Dongtan Nature Reserve is an important international wetland as well as a key area of coastal wetland biodiversity in China.The structure and function of wetland ecosystem based on Phragmites australis communis and Scirpus mariqueter communis has been changed by the invasion of S.alterniflora.The invasion has also seriously threatened biodiversity conservation.Controlling the expanding of the invasive species plays an important role in biodiversity conservation management at Chongming Dongtan Nature Reserve,Shanghai.To study the relationship between water depth of the waterlogging and the effect of controlling the expanding of S.alterniflora,we study the responses of S.alterniflora in terms of physiological and reproductive parameters to the gradient waterlogging through the combination of laboratory test and field investigation,in order to grasp the reasonable water depth and obtain useful insights into the control and management of this invasive plant in the nature reserve.The major findings are summarized as follows.1.The results of laboratory test showed that the height,the contents of chlorophyll a and b in leaves for the plants treated by 25cm waterlogging were significantly higher than those of the control(P＜0.05),while there was no significant difference in the sexual reproduction between the treatment and control.The height,the contents of chlorophyll a,b and soluble sugar in leaves for the plants treated by 50cm and deeper waterlogging were significantly lower than those of the control(P＜0.05),and there was no any blossoming and fruit bearing for the treated plants.After a 100-day treatment of 100cm waterlogging on S.alterniflora in laboratory test,there were no new-born stems appeared in the next spring.It could be concluded that waterlogging with low water depth(＜50cm) could promote vegetative growth of S.alterniflora,while waterlogging with water depth more that 50cm could effectively inhibit the vegetative growth and sexual reproduction of the plant.The depth of 50cm or more has been proved to be an effective water depth for controlling the expanding of S.alterniflora.2.In field investigation,we found that the there was no significant difference between height and the aboveground biomass for the plants treated in low water depth area(the water depth is 25-35cm) and those of the control(P＞0.05).By changing the biomass distribution and stretching the stem,S.alterniflora improved the situation of material exchange with atmosphere and adapted waterlogging with low water depth(≤30cm) so that the species can maintain its normal physiological processes.On the contrary,waterlogging with water depth deeper than 50cm can achieve an inhibitive effect on S.alterniflora.In field investigation,the height,density,LAI and the aboveground biomass for the plants treated in low water depth area(the water depth is 25-35cm) were significantly lower than those of the control(P＜0.05).S.alterniflora suffered from waterlogging with 50cm and deeper water depth.In summary,S.alterniflora had strong ability of anti-disturbance.Water depth was a key factor of waterlogging treatment and utilizing the proper water depth could gain the aim of controlling of the expanding of S.alterniflora.This sudy provided the scientific and technic support for the wetland management and protection of Dongtan Nature Reserve.