Ecological Responses Of Scirpus Mariqueter Population Dynamics To Heterogeneous Habitats In Chongming Dongtan Wetland

Yangtze River estuary is one of the typical wetland ecosystems in China,where Scirpus mariqueter population has widest distribution area with greatest ecological impacts.As a pioneer species in the coastal wetlands of the Yangtze River estuary,Scirpus mariqueter has important socio-economic and ecological values.However,in recent years,global climate change,biological invasion and human activities are seriously threatening the habits of Scirpus mariqueter.In this study,we take the dynamic characteristics of Scirpus mariqueter as the viewpoint,integrating plant morphological characteristics,ecological characteristics,physical and chemical indicators and environmental factors.The aim of this study is to explore the response characteristics and mechanisms of Scirpus mariqueter to the heterogeneous environment,as well as the main factors affecting the population dynamics of Scirpus mariqueter in Chongming Dongtan wetland,China.We conducted mutual transplantation experiments from different tidal habitats to reveal the adaptability of the population to heterogeneous habitats,in order to provide scientific basis for the cultivation and restoration of Scirpus mariqueter population,as well as the conservation and rational utilization of the salt marsh wetland communities.The main findings were as follows:1.The investment to sexual reproduction of Scirpus mariqueter increased with the increase of plant height,and its investment to asexual reproduction increased with the increase of population density.The eastern-side population had taller plants and higher seed setting rate,while the northern population grew weak with higher population density.The northern-side population had strong asexual reproductive ability with lower seed setting rate.In the relatively stable environments,Scirpus mariqueter preferred sexual reproduction,while in the relatively variable and disturbed environments,the robust asexual reproduction.Affected by the variable and disturbed environment,the pioneer Scirpus mariqueter population near the coastal line had a lower rate of sexual reproduction,mainly depending on the bulbs to realize the clonal reproductive colonization,while the populations in stable habitats,grew vigorously with taller plants,and higher investment to sexual reproduction.2.There were significant differences in the physicochemical properties of soils in the habitats of northern,southern and eastern sides of Chongming Dongtan wetland.The sequence of soil moisture,salinity,total organic carbon(TOC),total nitrogen(TN),and ammonia nitrogen(NH₄⁺-N)were northern-side>eastern-side>southern-side.The sequence of soil p H was southern-side>eastern-side>northern-side.The sequence of soil total phosphorus(TP)content was northern-side>southern-side>eastern-side.Soil nitrate nitrogen(NO₃^--N)content was low in each habitat.There were no significant differences in the physicochemical properties of soils between habitats in different locations in the same direction(northern-or southern-or eastern-side).The difference in soil salinity may be the main reason for the difference of growth and reproduction in the heterogeneous environments.In the range of salinity tolerance for Scirpus mariqueter,the plant height,aboveground biomass,belowground biomass,effective electron efficiency of the blade(F_v/F_m),maximum quantum yield of the blade(QY _max),population density,seeding rate,100-seeds weight and the antioxidant enzymes activities of corm all increased with the increase of soil salinity.This implied that the soil salinity(<3‰)facilitated the growth and reproduction of Scirpus mariqueter populations in the research area.3.The results of the mutual transplantation experiments revealed that the growth and reproductive characteristics of the original resident populations in each habitat had no significant effect on the transplanted populations.The difference in habitats after transplantation was the main reason that affected the difference in growth and reproduction of the transplanted populations.For the Scirpus mariqueter population,the intermediate habitat was a relatively stable habitat where all transplanted populations grew well,while the habitats near the coast line had the highest environmental stress and prevented the growth of the transplanted population.Among the transplanted populations,the original resident population far from the coast line had the strongest adaptability to various habitats.After being transplanted to the other habitats,it still showed strong adaptability,even exceed the original resident populations.The growth of the population far from the coast line was better than that of others,showing the most stable adaptability.During the growth of the transplanted populations in the new habitats,the increase of the total soil nitrogen content was beneficial to improve the adaptation of the transplanted populations to the new habitats,whereas,soil salinity became one of the main limiting factors to the growth of the transplanted populations.