Spectrofluorometric Characterization Of Soil Dissolved Organic Matter With Different Vegetation In Loess Plateau

Composition and structure of soil dissolved organic matter(DOM) are important indices of soil quality,and play significant roles in ecosystem functions by influencing carbon and nitrogen cycles. Studies of soil DOM quantities and fluorescent properties under different vegetation can provide scientific evidence for vegetation restoration on soil quality assessment. The traditional fluorescence spectra and three-dimensional fluorescence spectra are combined to study soil DOM. Humification indices from excitation-emission fluorescence spectra and synchronous fluorescence spectra were selected to assess source and structure of DOM, and the composition difference was researched by using 3-dimensional fluorescence spectral characteristics. The results are as follows:(1) In Loess Hilly Region soil DOM is mostly derived from mixing plants and microorganisms, the structures of DOM in Pinus tabulaeformia forestland is relatively simple due to low humification degree, in contrast to DOM in shrub land with higher humification degree and more complex matter structure.(2) The index of humus of DOM in saline-alkalisoil and swampmeadow in the depth of 10-50 cm are high,in the depth of 50-100 cm are low.The aromaticity of DOM in grassland is relatively low.The difference of humification degree of DOM in different soil depthin steppe land and sandy land are little.(3) In wind and water erosion region the structures of DOM in Populus simonii Carr,Salix cheilophila and Artemisia desertorum Spreng. Syst. Veg. forestland in the south-eastern slope have low levels of condensation,but the aromaticity of DOM in Caragana Korshinskii Kom forestland in the south-eastern slope,DOM in Stipa bungeana Trin. forestland on the top and DOM in Medicago forestland in the sunny slope are relatively high.(4) The uncultivated landshas high content of DOM in Loess Hilly-Gully Region.The content of DOM in Caragana Korshinskii Kom and Medicago forestland are higher than DOM in Armeniaca sibirica(L.) Lam. and Armeniaca vulgaris Lam.The content of DOM is higher in the depth of 0-20 cm,and the content of fulvic acid and humic acid are also high in surface soil.(5) The condensation degree of dissolved organic matter of mine soil in different parts is different. The condensation degree of DOM in Shanghe coal mine is high,but the humification degree of DOM in Xuemiaotan coal mine is low.The humification degree of DOM in Zhongneng coal mine and Yongle coal mine are at low level.The results of these studies illustrate that dissolved organic matter with with different types of soils under different vegetation has different composition and structure, so fluorescence techniques can be used to study the characteristics of soil DOM as a tool to reveal composition and condensation of water soluble organic matte.