Effects Of Spartina Alterniflora Invasion On Wetland Soil Organic Carbon Contents And Molecular Structure Characteristics

The Yellow River Delta is one of the most productive and carbon-fixing ecosystems in China.It plays a "carbon sink" function in the regional carbon cycle process,which is closely related to the evolution of the surface vegetation pattern.Since Spartina alterniflora was introduced into the Yellow River Delta in 1990,it rapidly expanded from northeast to southwest and became one of the main vegetation types in the Yellow River Delta.At present,domestic and foreign researches on the invasion of S.alterniflora on wetland soil are mostly focused on physical and chemical properties,microbial community structure and comparison of organic carbon content.However,few studies were concerned with the molecular structure characteristics of SOC due to the invasion.The change of organic carbon characteristics and functional groups failed to effectively link with the carbon turnover process at the macroscopic scale.Based on this,this study took mudflat,native vegetation(Phragmites australis,Suaeda salsa,Tamarix chinensis Lour)and S.alterniflora wetlands with different invasion years in the Yellow River Delta as the research objects.Using field surveys and laboratory analyses,phospholipid fatty acids(PLFAs),Fourier Transform Infrared Spectroscopy(FTIR)and Thermal Pyrolysis-Gas Chromatography Mass Spectrometry(Py-GC/MS)technology,we compared the difference of soil physical and chemical properties and microbial community structure under the native communities and Spartina alterniflora communities,and explored the effect of S.alterniflora invasion on soil organic carbon content,functional groups and molecular structure characteristics of soil organic carbon pool,and clarified the dominated factors affecting the changes of wetland SOC to evaluate the impact of S.alterniflora invasion on soil carbon stocks stability stability.Research indicates:PLFAs analysis showed that S.alterniflora invasion significantly increased the microbial biomass of the wetland soil in the Yellow River Delta,and also changed the community structure of the wetland soil microbes.At the beginning of the invasion,the total abundance of S.alterniflora PLFAs,Gram-negative bacteria(G-),Gram-positive bacteria(G+),bacteria(B)and fungi(F)was significantly lower than that of Phragmites australis wetlands,higher than Other types of wetlands,and this microbial indexes were significantly positive correlation with the invasion years of S.alterniflora.The abundance after 20 years of invasion was significantly higher than that of mudflat and all native vegetation wetlands.S.alterniflora invasion significantly resulted in the increase of the contents of total soil organic carbon(SOC),dissloved organic carbon(DOC)and easily oxidizable organic carbon(EOC),increased SOC density and soil carbon stocks in the Yellow River Delta wetlands.In the initial year,the invasion of alterniflora did not cause significant changes in soil organic carbon content under the mudflat and native vegetation communities.With the increase of the invasion years,the soil organic carbon content significantly increased.After 7 years of invasion of S.alterniflora,the organic carbon content reached the maximum.Correlation analysis showed that SOC,EOC and DOC were significantly positive correlated with S.alterniflora invasion years.FTIR analysis showed that S.alterniflora invasion did not significantly change the major functional groups of SOC and DOC in the Yellow River Delta wetland,but changed the abundance of SOC and DOC functional groups in soil.The DOC infrared maximum absorption peaks are located at 3395cm-1 and 1140cm-1,which are the symbol of carbohydrates;the SOC infrared maximum absorption peaks are located at 1680cm-1 and 1285cm-1,which are the indicator of aromatic compounds.Py-GC/MS analysis showed that S.alterniflora invasion significantly increased the proportion of SOC aliphatics,polysaccharides and sulfur compounds in the Yellow River Delta wetland,and significantly reduced the relative abundance of SOC aromatic compounds.The proportion of polysaccharides and sulfur-containing compounds in the DOC were significantly increased and the proportion of alkyl compounds were decreased.With the increase of the invasion period of S.alterniflora,the differences in the composition of DOC and SOC organic compounds increased significantly compared between the mudflat and native vegetation soil.The proportions of SOC recalcitrant components followed the order:mudflat>T.chinensis Lour>S.salsa>P.australis.After S.alterniflora invasion,the proportion of SOC active components was significantly increased,and the proportion of SOC recalcitrant components was decreased,and the proportion of SOC recalcitrant components was significantly negative correlated with the years of alterniflora invasion.The main influencing factor of SOC active components in the Yellow River Delta wetland is salt content,and the main influencing factor of SOC recalcitrant components is fungal biomass.The invasion of S.alterniflora significantly reduced the salt content of the Yellow River Delta and increased the fungal biomass,resulting in a decrease in the stability of the soil carbon pool in the Yellow River Delta wetlands.