北京森林土壤富里酸亚组分的表征及荧光指标分析

Characterization and Fluorescence Index Analysis for Forest Soil Fulvic Acid Sub-Fractions in Beijing

为探究土壤FA(富里酸)的结构组成及其腐殖化和芳香性特征,采用SFS(同步荧光光谱)技术结合FRI(荧光区域积分)、DSFS(导数荧光光谱)及PCA(主成分分析)对土壤FA亚组分的荧光光谱特征及荧光指标间的相关性进行了分析.利用XAD-8吸附树脂结合初始p H为3、5、7、9和13的Na4P2O7(焦磷酸钠)缓冲溶液逐步洗脱技术将土壤FA分别分级得5种亚组分(FA_3、FA5、FA7、FA9和FA_(13)).结果表明:(1)FA_3-FA_(13)的SFS体现3类荧光峰,分别代表类蛋白、类富里酸和类腐殖酸物质.FA_3和FA5含有含量相近的类蛋白、类富里酸和类腐殖酸物质,而FA7-FA_(13)含有的主要成分是类蛋白物质;同时,FA7-FA_(13)的类富里酸和类腐殖酸较FA_3和FA5更为复杂,且FA7-FA_(13)含有更多易降解的单环芳香族化合物.(2)FA_3和FA5的类酪氨酸和类色氨酸物质被识别,且FA7-FA_(13)的类色氨酸含量明显大于类富里酸和类腐殖酸含量.(3)FA_3-FA_(13)光谱荧光强度指标(I240/I340、I240/I450、I340/I270、I450/I270和I450/I340)的对比分析表明,FA_3和FA5的腐殖化程度和芳香性均大于FA7-FA_(13).(4)荧光指标AFLR/A、AHLR/A、S270-340、S270-450、A2/A1和A3/A1可作为指示亚组分芳香性的优化指标,且AHLR/A、A2/A1和A3/A1可作为最佳指标反映亚组分的腐殖化程度.研究显示,土壤FA亚组分的结构表征及荧光指标分析为后续FA亚组分与环境污染物相互机理研究提供依据,为探究有机质的结构特性和环境行为提供理论支撑.

In order to explore the structures and compositions,and the characteristics of humification and aromaticity of soil fulvic acid（ FA）,the synchronous fluorescence spectra（ SFS） technique combined with fluorescence region integral（ FRI） method,derivative synchronous fluorescence spectra（ DSFS） method and principal component analysis（ PCA） were utilized to study the spectral characteristics and the correlations among fluorescence indexes for FA sub-fractions. The XAD-8 adsorption technique coupled with the stepwise elution using Na4 P2 O7 buffers with initial p H values 3,5,7,9 and 13 were used to separate the FA into five sub-fractions： FA3,FA5,FA7,FA9 and FA13,respectively. The results indicated that three fluorescence peaks were shown in the SFS of FA3-FA13,which represented the protein-like,fulvic-like and humic-like materials,respectively. FA3 and FA5 contained similar content of protein-like,fulvic-like and humic-like materials,while protein-like materials were the primary components in FA7-FA13. Meanwhile,FA7-FA13 contained more complex structures in fulvic-like and humic-like materials than those in FA3 and FA5,and FA7-FA13 had more biodegradable monocyclic aromatic compounds. Tyrosine-like and tryptophan-like materials in FA3-FA5 were identified by DSFS method.Additionally,the content of tryptophan-like materials in FA7-FA13 was significantly higher than that of both fulvic-like and humic-like materials. The comparative analysis of fluorescence intensity indexes（ I240/I340,I240/I450,I340/I270,I450/I270 and I450/I340） for FA3-FA13 indicated that FA3 and FA5 had higher humidification degree and aromaticity than FA7-FA13. Further,the AFLR/A,AHLR/A,S270-340,S270-450,A2/A1 and A3/A1 could be optimized indexes for indicating the aromaticity of FA sub-fractions,and AHLR/A,A2/A1 and A3/A1 were the best indexes for reflecting their humidification degree. The study shows that the characterization and fluorescence index analysis of soil FA sub-fractions could provide the basis for the future interaction studies between FA sub-fractions and environmental pollutants and the theoretical supports for exploring the structural properties and environmental behaviors of dissolved organic matter.