黄土丘陵区不同植被下土壤可溶性有机物的荧光特征研究

【目的】土壤水溶性有机质的组成和结构是土壤质量的重要判别指标,具有重要的生态意义。研究黄土丘陵地区不同植被下土壤水溶性有机物的数量和荧光结构特征,可以为该地的植被修复及土壤质量评价提供科学依据。【方法】利用传统荧光和三维荧光技术,选取激发发射荧光光谱、 同步荧光光谱得到的腐殖化指标对土壤水溶性有机物的来源和结构进行评估,通过三维荧光技术探究不同植被下土壤水溶性有机物之间组分的差异。【结果】辽东栎(Quercus liaotungensis)和油松林(Pinus tabulaeformia)地具有较高的水溶性有机物含量,含量均为0.16 mg/g; 而荒坡地和农地的水溶性有机物较低,分别为0.04和0.05 mg/g,灌木荆条(Vitex negundo var. heterophylla )和狼牙刺(Sophora viciifolia)林地的含量介于两者之间。发射激发荧光光谱、 同步荧光光谱以及三维荧光光谱表明土壤水溶性有机物大多来源于植物和微生物的混合作用; 油松林地的水溶性有机物结构较简单、 腐殖化程度较低; 而灌木林地的水溶性有机物结构较为复杂、 腐殖化程度较高。从不同植被下土壤水溶性有机物的组成来看,蛋白类的物质差异不明显; 油松和辽东栎林地土壤水溶性有机物的类酪氨酸蛋白质、 类色氨酸蛋白质、 类溶解性微生物代谢产物含量较高,灌木林地较低。最主要的差异是富里酸类和胡敏酸类物质,油松林地的水溶性小分子量的富里酸类物质占主导地位,而灌木林地的水溶性有机物芳香化程度较高,农地和抛荒地类富里酸物质和类胡敏酸类物质含量的比值最低,其水溶性腐殖质的缩聚度高。油松、 辽东栎林地水溶性有机物由于植物残体分解形成的富里酸较易被氧化,同时阴坡林地较高的含水量使得这些产物较难缩合; 而灌木林地和农田及荒地较为干旱,枯枝落叶少,腐殖酸有充分时间进行缩合,导致了水溶性有机物的高芳香化和腐殖化。【结论】不同植被下的土壤水溶性有机物的组成和结构是存在差异的,同时说明荧光技术可用于揭示水溶性有机物的组成和缩合特性研究。

Spectrofluorometric characterization of soil dissolved organic matter under different vegetation in Loess Hilly Region

Objectives]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. Methods] 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. Results] There are high contents of DOM with 0. 16 mg / g for Quercus liaotungensis and Pinus tabulaeformia forestland, compared to farm and uncultivated lands with the contentss from 0. 04 to 0. 05 mg / g, and the DOM contents of shrub forest land such as Vitex negundo var. heterophylla and Sophora viciifolia are in the above range. The excitation-emission, synchronous, and three-dimensional fluorescence spectra show that 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. There are no obvious differences for protein-like matters for different vegetation and land utilization. The DOM in Quercus liaotungensis and Pinus tabulaeformia forestland has high contents for tyrosine-like protein, tryptophan-like protein, and some matters associated with biological production, but these materials are low in shrub forestland. The major differences are in humic acid-like and fulvic acid-like matters. The small molecular weight fulvic acid-like matters are predominant for soil DOM in Pinus tabulaeformia forestland, but DOM under shrub forest land has a higher level of aromatic. The ratios of fulvic acid-like and humic acid-like matters for farm and uncultivated lands are the lowest among soils with that different ground vegetation, and the DOM is with high degree of condensation. The DOM from Quercus liaotungensis and Pinus tabulaeformia forestland is difficult to condensate as a result of fulvic acid-like matters from decomposition of plant residues more easily oxidization, and higher the moisture in shady woodland. The degrees of aroma and humification of DOM from shrub, cultivated and uncultivated lands are rather high with sufficient time for condensation due to arid environment and less litter sources. Conclusions] The results of these studies illustrate that soil dissolved organic matter with 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.