Characteristics Of Plant Communities And Competitive Ability Of Spartina Alterniflora Along Elevational Gradient In The Salt Marshes Of Hangzhou Bay

Coastal salt marsh wetlands which located at the ecotone between land and ocean are extremely sensitive to sea-level rise caused by global climate change.Sea-level rise has been considered as one of the important reasons for the habitat loss of salt marsh wetlands,biological communities change and ecosystem service function reduce.Moreover,the disturbance frequently and single vegetation make the salt marsh wetlands ecosystem to be one of the most vulnerable ecosystems.In China's coastal salt marsh,exotic species Spartina alterniflora is expanding and invading to a large area.In order to study the evolution of vegetation community in our country's salt marsh wetland under the pressures of sea level rise and biological invasion,we took the Hangzhou Bay wetland as an example.The study was proceed based on the elevation gradient,the field transplanting experiments and the competition experiments were mainly carried out to explain the growth performance of indigenous plants(Phragmites australis and Scirpus mariqueter)and exotic species S.alterniflora along to the elevation gradient change,to study the competitive response to different elevation of those two indigenous plants compared with the S.alterniflora,and to reveal the impact of sea level rise on the invasion of two indigenous plants.The results will give an instruction to the management and controlment of invasive plants,and provide theoretical basis to the protection and sustainable utilization of salt marsh wetlands in China.The main results are as follows:1)Field investigation shows that: with the elevation decrease,the tidal flat flooding frequency and flooding time increase,the soil moisture content and salinity tends to increase as well,but the soil oxidation and reduction potential tends to decrease.2)Transplanting experiments from high elevation to low elevation show that: the plant height,plant number,aboveground and belowground biomass of the indigenous P.australis in the high tide flat were significantly higher than those in the other tidal flat;S.mariqueter exhibited the best growth performance in the low tidal flat,but it couldn't be grown in mudflat;The plant height and aboveground biomass of S.alterniflora in the middle tidal flat were significantly higher than those in the middle and low tidal flats.3)Competitive experiments between S.alterniflora and P.australis at high and middle tidal flats show that: both in the high and middle tidal flats,the aboveground and belowground biomass for the S.alterniflora which in no competition of P.australis are significantly higher than those for the S.alterniflora which in competition of P.australis.Above the ground,the competitive intensity between S.alternifrila and P.australis in the high tidal is stronger than that in middle tidal flat.While in the belowground,the competitive intensity of S.alternifrila and P.australis gives no difference in different tidal flats.The above results show that as the elevation decreases,the competition performance of S.alterniflora in the aboveground tends to increase,and the invasibility to P.australis increases.4)Competitive experiments between S.alterniflora and S.mariqueter at middle and low tidal flats show that: the S.alterniflora aboveground biomass exhibits outstanding difference between the experiment without competition sample and the experiment with competition sample in the middle tidal flat,while there is almost no difference in the low tidal flat for those experiments;Interestingly,the results are opposite for the belowground biomass.The competition intensities of S.mariqueter to S.alterniflora at middle and low tidal flats are relative low.It means that S.alterniflora shows a competitive advantage both in middle and low tidal flats.The above results indicate that the decrease of elevation will enhance the belowground competitive ability of S.mariqueter to S.alterniflora,but it couldn't affect the whole competitive advantage of S.alterniflora.