A Study On Population Restoration Techniques Of Scirpus Mariqueter In The Newly Formed Tidal Marsh

As one of the most typical tidal wetland ecosystem in coastal zone of China,the Yangtze Estuary is also the ecological sensitive area of international significance and migratory bird habitat.The constructive species in the Yangtze Estuary and Chinese endemic community of Scirpus mariqueter,which provides irreplaceable ecosystem services for protecting embankments and bird habitats,promoting deposition,fixing carbon,purifying the environment,has been shrunk by the mounting reclamation and rapid expansion of exotic Spartina alterniflora since the 1990s.The conservation and restoration for S.mariqueter shows extremely important and urgent,contributing to maintaining biodiversity and the stability of the coastal wetland ecosystem,while complex environmental conditions including hydrology,sedimentation and topographic factors represent crucial challenges on the ecological restoration project.The study proposed and optimized feasible revegetation strategies and key technology system,which could provide restoration projects and sustainable development of coastal wetland ecosystem with scientific basis and suggestions.Based on the project of ecological control of S.alterniflora and improvement of birds habitats at Chongming Dongtan wetland,experiments involving S.mariqueter revegetation were conducted by using three plant materials(seeds,seedlings and corms),different levels of planting density(low density,middle density,high density)and different experimental regions(with different hydrodynamic conditions and sediment deposition dynamics)in the newly formed tidal marshes in order to test the planting effects(survival rate and plant density).Independent-samples t-test,one-way ANOVA,two-way ANOVA and non-parametric test were conducted in statistic analysis.The impacts of wave energy density and sediment deposition dynamic on the population establishment of S.mariqueter were also measured and analyzed in different experimental regions.The main research conclusions were as follows:(1)The revegetation strategies involving seeds and seedlings were conducted in the first.The results indicated that the rate of seed germination reached high level in 0-15 cm buried depth under laboratory conditions,especially topping at 66.80%when planted in 5-cm depth.The sediment burial depth(buried stress)of approximately 20 cm might be a tolerant threshold for the survival of S.mariqueter seedlings because of the low germination rate(2.4%).However,the rate of germination(1.13%)and seedling emergency(0.45 ind-m-2)was extremely low in the field(in 5-cm buried depth)even with high planting density(4000 ind m'2),while the planting methods of low density(1000 ind·m-2)and middle density(2000 ind m-2)failed in emerging ultimately,mainly due to the heavy burial stress of sediment deposition in the tidal flat.Therefore,recovery strategies based on seed showed ineffective in the newly formed tidal marshes during the first growing season,while the subsequent development of seeds needed further in-depth investigation.Based on four levels of patch size(50 seedlings,200 seedlings,400 seedlings and 800 seedlings),the experiments involving S.mariqueter revegetation using seedling(obtained from seed germination)planting approach turned out to be a failure in the newly formed tidal marsh in spite of the high survival rate at the early growing stage(from May to June).Because of the strong stress from sediment deposition(accumulated accretion exceeded 11 cm between July and August)and tidal current,all the new seedlings were killed eventually.(2)Two experimental regions with different hydrodynamic conditions and sediment deposition dynamics(the wave energy density and sediment deposition fluctuations of Site-1 showed less and gentler than Site-2)were selected at Chongming Dongtan and the field experiment of S.mariqueter corm revegetation was examined.The soil microcosms consisting of corms of S.mariqueter were dug by soil augers(diameter of 7.5 cm)and the depth of corms was 15 cm.Three levels of initial planting density(low planting density-15 ind m-2,medium planting density-30 ind m-2,high planting density-60 ind-m'2)were conducted to assess the cost-effectiveness in ecological restoration project.The results indicated that the differences in sedimentary rates and tidal wave energy during the initial establishment period significantly influenced the outcome of succession.Furthermore,the environmental conditions and approaches of planting would be deciding factors affecting the success/failure of revegetation.The wave energy density and sediment deposition fluctuations of Site-1 showed less and gentler than Site-2.During the early growing season,a moderate sedimentary accretion rate(3.4-5.1 cm per month)led to the persistence of corms,which,in turn,benefited the colonization of S.mariqueter seedlings by vegetative tillering and the growth of rhizomes underground.In Site-1,the survival rate and plant density under high initial planting density treatment between the early and middle growing seasons were higher than that under low and middle initial planting density treatment significantly(P<0.05),while the survival rate topped at 39.5%in the early growing season and the plant density topped at 74.6 ind-m'2 in the middle growing season.In Site-2,the survival rate and plant density under high initial planting density treatment throughout the growing season were higher than that under low and middle initial planting density treatment significantly(P<0.05),while the survival rate topped at 49.6%in the early growing season and the plant density topped at 35.6 ind·m 2 in the middle growing season.It is noteworthy that the survival rate and plant density in Site-2 followed a sustained downward trajectory since May under the strong stress of sediment deposition and tidal flow,which resulted in the failure of population establishment.The plant growth(shoot density and plant height)were significantly influenced by the site selection and initial planting density,and their interaction(P<0.01).At the same time,a medium planting density might be a cost-effective way to restore S.mariqueter community in the newly formed mudflats,because the high-level shoot density(approximately 200 ind·m'2)was achieved with the medium planting density relative to the high planting density(P>0.05),while the cost input for the acquisition and planting of corms was proportional to the planting density.In conclusion,the planting technique with soil microcosms consisting of corms might be feasible for revegetation of S.mariqueter in the newly formed mudflats.The study suggested that incoming large-scale revegetation engineering could take the disturbances of hydrodynamic conditions and sediment deposition dynamics,the rules of reasonable site selection(the tidal marsh in the south of the project area of ecological control at Chongming Dongtan wetland),and cost-effectiveness of planting strategies(30 ind·m-2-medium initial density with corm planting)into concern carefully in the newly formed tidal marsh.