The Response Of The Composition And Structure Of Soil Dissolved Organic Matter To The Invasion Of Spartina Alterniflora In The Yanghe Estuary Wetland Of Jiaozhou Bay

Taking the tidal flat wetland in the Yanghe estuarine wetland as case study,this study explored the distribution status and expansion rate of invasive species Spartina alterniflora.Then we analyzed the distribution characteristics and relevance of dissolved organic carbon（DOC）,dissolved organic nitrogen（DON）,and dissolved organic phosphorus（DOP）with different time series of invasion,and the application of spectroscopy to explore the effects of S.alterniflora invasion on wetland soil DOM structure.The conclusions of our study are as follows:（1）The degree of influence of different invasive years of S.alterniflora in Yanghe wetland on soil dissolved organic matter（DOM）content is different.The average DOC content in the MF,SAF-1,SAF-5,and SAF-8 plots were 35.67,47.31,130.67,and 168.99 mg/kg,respectively.In the vertical direction,the DOC content in the soil surface of the MF and SAF-1 plots was the highest.The DOC content in the SAF-5 and SAF-8 plots was the highest in the 10²0 cm soil layer.The content of DON and DOP decreased with the increase of invasion time of S.alterniflora.The difference between SAF-5 plot and SAF-8plot was not obvious.In the vertical direction,the content decreased with the deepening of soil profile.The litter and root distribution of S.alterniflora are the main reason for the change of DOM.（2）The total organic carbon（TOC）,total nitrogen（TN）and total phosphorus（TP）levels increased with the intensification of invasion time.In the vertical direction,the trend of TOC and TP content changes gradually downwards along the profile.There was no obvious change in the TN content in the vertical section.The S.alterniflora as a C₄ plant can promote the accumulation of TOC,TN and TP.The nutrients in the soil are affected by tidal action and arbuscular mycorrhizal fungi are the main reason for the change of TOC,TN and TP.At the same time,the changes of pH in the four plots were gradually decreased;in the vertical direction,the pH changes are gradually decreased.The soil bulk density before and after S.alterniflora invasion was SAF-5<SAF-8<SAF-1<MF;the vertical distribution law gradually increased downward along the profile.The change trend of soil moisture content in wetland was reversed with the soil bulk density.Soil DOC is significantly correlated with pH,water content,bulk density and TOC.The smaller the soil bulk density,the higher the water content,the greater the porosity and the improved ventilation conditions,which is beneficial to the activities of soil animals and aerobic microorganisms.As the falling matter decomposes,the DOC that is soluble in water in the soil organic matter will also increase.The soil DON and DOP were significantly correlated with pH,TN and TP,respectively.DON and DOP were components of soluble organic matter.So far,both the soil organic layer and the newly litter layer may be sources of soluble organic matter.（3）The molecular weight and molecular quantity of DOM before and after the invasion changed,and the change was mainly concentrated in the macromolecular substances（aromatic,protein-like substances）which are difficult to degrade,and the number of molecules increased with the increase of the invasive years.It can be seen that DOM molecular weight,functional group and complexity are sensitive to S.alterniflora invasion,mainly related to plant photosynthesis and root exudates,leaching or decomposition of surface organic matter,microbial processes of soil organic matter.（4）The composition and structure of the DOM are sensitive to the response of S.alterniflora.Mainly in the soil,the content of DOC,DON and DOP increased or decreased after the invasion of S.alterniflora,while the molecular weight increased and the structure became more complicated in DOM.