Preliminary Studies On Autotoxicity Potentials Of Invasive Smooth Cordgrass(Spartina Alterniflora Loisel.) In Jiuduansha Wetland

In this study, exotic Spartina alterniflora in Jiuduansha islands were researched. With analyzing Remote-sensing images of different times and field investigation, by time converting to space method, the autotoxicity of S. alterniflora community, variation regularity of autotoxins in soil with the increase of invasion time and the source of autotoxins in soil of S. alterniflora community was studied to discuss the possibility of S. alterniflora control by using its autotoxicity. And then provide some scientific suggestion for the restoration and protecting the Jiuduansha wet land national nature reserve from invasion of S. alterniflora.Seeds, living plants and litters of S. alterniflora, soils of S. alterniflora community were collected and taken back to our library. Six concentration levels of soil aqueous extracts were established to examined the autotoxic effects of soil aqueous extracts on seed germination and seedling growth of S. alterniflora. To investigate the variation regularity of autotoxins in soil, we tested kinds and contents of autotoxins in soils with different invasion time and different depth. Besides, in order to prove the source of autotoxins in S. alterniflora community, we implemented litter degradation experiment and root secretion extraction experiment. The results we acquired were as follows:(1) Autotoxicity is existed in S. alterniflora community. At low concentrations(<0.3), soil leaching liquor promoted seed germination rate and seedling growth; Soil leaching liquor inhibited seed germination rate and seedling growth at high concentrations(>0.3), and the inhibition enhanced with the increase of soil leaching liquor concentrations. Activities of SOD, POD and CAT in germinated seeds and seedlings were influenced by soil leaching liquor with all concentrations, and the inhibitory influence only existed at high concentrations(>0.5).(2) Soil can reduce the toxicity effects of soil leaching liquor on S. alterniflora seedlings. Compared with sand culture, soil culture has lighter toxicity effects on seedlings.(3) The main chemical substance in soil aqueous extracts and methanol extracts of S. alterniflor community root’s secretion was long-chain fatty acid. Among of them, palmitic acid, stearic acid and oleic acid have been identified as autotoxins in the study of other species.(4) With the increase of soil depth, the content of autotoxins in soil decreased at first and then increased. Under the condition of the same depth, the content of autotoxins in rhizosphere soil is higher than non-rhizosphere soil. With the increase of invasion time, the content of autotoxins in soil changes regularly. In the topsoil, contents of palmitic acid and stearic acid increase with the increase of invasion time. In deep layer soil, palmitic acid and stearic acid have higher contents when the invasion time between 2 year and 7 years; palmitic acid and stearic acid have lower contents and level off when the invasion time more than 10 years.(5) The content of autotoxins in soil of S. alterniflor community is connected with elevation, above-ground biomass and litter amount. The content of specific autotoxin may be affected by one factor or multi-factor. The content of oleic acid is mainly affected by litter amount.(6) Residue decomposition and root secretion of S. alterniflor can produce palmitic acid, stearic acid, oleic acid and other ong-chain fatty acids. Autotoxins in soil of S. alterniflor community mainly come from residue decomposition and root secretion of S. alterniflor.