| The reclamation area of Chongming Island account for 60%of the total reclaimed area of Shanghai Municipality.Because of the tidal dam block cut off the tidal water supply,soil showed obvious drought.Coupling with human activities(farming,reservoir construction et al.),which changed the topography and vegetation distribution of coastal reclaimed wetland and then changed the hydrological conditions and salt circulation.Therefore,the hydrological conditions and soil physical and chemical properties of coastal reclaimed wetland were different from the natural tidal wetland.Water table and soil salinity were the key factors to limit the growth and distribution of plants in the coastal reclaimed wetland.In order to preserve the original ecological landscape of reclaimed wetland,how to regulate and control water table and soil salt of wetland had become the focus of research.For better understanding of P.australias's role in water-salt manipulation and wetland vegetation restoration,this research aimed to study the relationship between photosynthesis and growth characteristics of the reed and soil water-salt indicators.The main results of this dissertation were as follows:(1)Water table and soil electrical conductivity had obvious seasonal variation in Chongming dongtan wetland.Based on the monthly variation of water table,four stages were divided across a year,they were:?The water table decreased slightly during March to April.?Water table rose rapidly and sample plot 3,4,5 and 6 even flooded.?The water table decreased significantly during July to August.?The water table rose gradually during September to November.The variation of soil salinity in the whole growth season can also be divided into four stages.The first stage was salt accumulation period in spring(March to May)and the surface soil salinity rose slightly.The second stage was desalination period in rainy season(June to July)and the surface soil salinity decreased gradually.The third stage was salt accumulation in late summer and early autumn period(August to October)and soil salinity increased significantly.The fourth stage was desalination period in late fall and winter and soil salt content decreased gradually.In the study area,there was a significant negative correlation between water table and soil electrical conductivity,and the correlation coefficient was-0.457(P<0.01).Increasing annual average water table of reed community was beneficial to increase the leaching of soil salt,which can alleviate the salt stress damage.(2)The net photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(gs)of Paustralias had a significant positive correlation with water table(p<0.01),respectively,and had a significant negative correlation with soil electrical conductivity.Intercellular CO2 concentration(Ci)had no significant correlation with water table and soil electrical conductivity.When water table was higher than-50 cm,the net photosynthetic rate decreased and Ci increased with the decrease of water table.Non-stomatal limitation may be the reason of the decrease of net photosynthetic rate.When water table was lower than-50 cm and the soil electrical conductivity was higher than 10 mS/cm,the transpiration rate(Tr)decreased rapidly,whereas the water use efficiency(WUE)increased continuously.Reed can increase water use efficiency(WUE)and enhance the ability of stress tolerance by controlling the exchange ratio of CO2 and water vapor under the condition of salt stress and drought stress.P.australias adapted to decreased water table accompanied by a higher soil electrical conductivity with lower maximum net photosynthetic rate(Pmax),dark respiration(Rd),light compensation point(LCP)and light saturation point(LSP).The decrease of water table and the increase of soil electrical conductivity significantly inhibited the photosynthetic physiological activities of P.australias,and weakened the ability of reed to use weak light in the morning and evening.(3)There was a significant positive correlation between the plant height,stem diameter,leaf area per plant,aboveground biomass per plant and water table(P<0.05).Leaf numbers had no significant correlation with water table.The population density,leaf area index and aboveground biomass per unit area also had a significant positive correlation with water table respectively(P<0.01).P.australias showed low population density,low leaf area index and low biomass at low ground water depth(<5 cm),and high population density,high leaf area index and high biomass at high ground water depth(>0 cm).There was a significant negative correlation between the plant height,stem diameter,leaf numbers,leaf area per plant,aboveground biomass per plant and water table(P<0.05).The reed growth index increased with the increase of the soil conductivity below 3 mS/cm,but decreased rapidly with the increase of the soil conductivity above 3 mS/cm.The.relationship between soil electrical conductivity and the population density,leaf area index and unit area aboveground biomass was consistent with the Gauss model.The ecological thresholds zone of reed growth to soil electrical conductivity was[0.615,7.035](mS/cm),and the optimum ecological thresholds zone was[-0.92,0.08](mS/cm).In conclusion,with reed photosynthetic physiological indexes as the reference,the water table of study area in Reed Growing period should be controlled above-50cm and the salinity should be controlled under 10 mS/cm.With reed growth index as the reference,the water table of study area in Reed Growing period should be controlled above 0cm and the salinity should be controlled in[2.22,5.43](mS/cm). |
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