Leaching Process And Spectral Characteristics Of Dissolved Organic Matter From Plant Litter In Dongtan Salt Marsh,Chongming

Litter decomposition is a key component of carbon and nutrient cycling in salt marsh wetlands,and the leaching process of litter during flooding is an important way for dissolved organic matter（DOM）export.Taking the Chongming Dongtan wetland as the research object,this paper studied the litter leaching process of four typical salt marsh vegetation（Carex scabrifolia,Scirpus triqueter,Scirpus mariqueter,Phragmites australis Spartina alterniflora）in 48 hours,and analyzed the release characteristics and influence mechanism of dissolved organic carbon（DOC）,total nitrogen（TN）,chromophoric dissolved organic matter（CDOM）including their fluorescence components.UV-Vis absorption spectra and three-dimensional fluorescence spectra were used to analyze the structural characteristics of DOMThe conclusion is as follows:（1）By the end of the 48 hour simulation experiment,for the low temperature environment,the cumulative release of DOC,TN,CDOM(characterized by a₃₅₅)are3.50～30.68 mg?g^-1,0.30～3.69 mg?g^-1,3.08～48.24 m^-1 respectively;and for the high temperature environment,the cumulative release of DOC,TN,CDOM(characterized by a₃₅₅)are 1.30～31.41 mg?g^-1,0.20～1.10 mg?g^-1,1.65～37.67 m^-1 respectively.There is a power function relationship between the cumulative release of DOC and soaking time t,and the cumulative release of TN at low temperature as well as CDOM content also has power function relationship.Both of DOC,TN and CDOM increase rapidly in the initial stage,slowed down or even slightly decreased in the later stage.The content of CDOM is synchronous with the change of DOC,but there are significant differences in the linear correlation between CDOM and DOC in different plant species and tissues of litter as well as different temperature conditions.（2）There are significant differences in DOM leaching amount among different plant species and tissue types of litter,which indicate that the composition of initial litter had a significant impact on DOM leaching.In the early stage of litter leaching,nitrogen is more likely to leach than organic carbon.There is no significant correlation between the maximum cumulative release of DOC and TN and the C/N ratio of litter substrate,indicating that the C/N ratio of litter itself is not the major factor that affects the leaching of litter.After 24 hours of leaching,the increase rate of DOM release in high temperature environment is significantly lower than that in low temperature environment,which may be due to different microbial activities at different temperatures.（3）The proportion of aromatic substances in DOM which are leached by litter of different plant species and tissue types is different,and the aromaticity of DOM fluctuates more in high temperature environment.In the process of leaching,fulvic acid with low molecular weight is the main component of litter’s CDOM.The molecular weight of litter’s CDOM is consistent with that of terrestrial CDOM.（4）The results of fluorescence region integral（FRI）and parallel factor analysis（PARAFAC）showed that all fluorescence components were positively correlated with DOC,TN and CDOM,indicating that the dynamic changes of fluorescence components are consistent with those of DOC,TN and CDOM,and are significantly affected by the properties of litter substrate.The contribution rate of fluorescence components of each litter change little with time,indicating that the structure of CDOM did not change significantly in the early stage of litter leaching,but there are significant differences in the contribution rate of fluorescence components among different plant species.In this experiment,PARAFAC is more accurate than FRI.This study showed that there is a rapid DOM release process in the salt marsh plant litter during the tidal inundation period,which will affect the content and structure of DOM in the salt marsh and the surrounding water,and further affect the material cycle process of the whole region.