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    基于EEM-PARAFAC分析冻融作用对高寒泥炭湿地土壤溶解性有机质的影响

    Analyzing the effects of freeze-thaw on dissolved organic matter in alpine peat wetland soil based on EEM-PARAFAC

      摘要
    • 摘要:
        目的  全球气候变暖加速了土壤冻融格局的改变，而冻融作用又对土壤溶解性有机质（DOM）产生深刻的影响。
        方法  以高寒泥炭湿地土壤为研究对象，采用室内模拟冻融的方式开展了两种冻融条件下（日冻融：−3 ℃/5 ℃，12 h/12 h，30次；深度冻融：−24 ℃/5 ℃，20 d/10 d，1次）的试验研究，基于紫外−可见吸收光谱（UV-vis）和三维荧光光谱结合平行因子（EEM-PARAFAC）分析探究土壤DOM数量和质量的变化。
        结果  （1）经过30 d培养后，两种冻融处理均显著提高了高寒泥炭湿地土壤溶解性有机碳（DOC）的含量，日冻融和深度冻融条件下土壤样品的DOC含量分别为183.26和187.06 mg/kg，相比于对照组分别增加了18.80%和21.26%（P < 0.05）。（2）不同冻融条件下的土壤DOM的紫外−可见吸收曲线线型差异较小，无明显特征吸收峰，且显示出吸光度随波长呈指数衰减的趋势，但经冻融处理的样品出现了明显的红移现象。（3）两种冻融处理均使得土壤DOM的腐殖化指数（HIX）值（从4.42增加至11.73和17.10）、254 nm处的单位比色皿光程下的紫外吸收值（SUVA254）（从1.35 mg/（L·cm）增加至1.37和1.40 mg/（L·cm））以及A253/A203值（0.38增加至0.40和0.43）增大，波长275 ~ 295 nm处光谱斜率系数减小（从13.34 μm−1减小至13.23和12.91 μm−1）。（4）EEM-PARAFAC鉴别出的荧光组分有类富里酸物质、类腐殖酸物质、溶解性微生物代谢产物和类蛋白物质，冻融改变了土壤DOM的组成以及各组分的贡献率。对照组土壤DOM组分C1、C2和C3的贡献率分别为37%、32%和31%；日冻融条件下，组分C1、C2和C3的贡献率分别为41%、34%和 25%；深度冻融条件下，组分C1、C2和C3的贡献率分别为44%、35%和 21%。
        结论  冻融改变了土壤DOM的数量和质量，表现为DOC含量的增加和腐殖化程度的提高。

       

      Abstract:
        Objective  Global warming has accelerated changes in soil freeze-thaw patterns, and it is important to clarify the effects of freeze-thaw on dissolved organic matter (DOM) in soils.
        Method  Experimental studies were conducted in alpine peat wetland soils under two freeze-thaw conditions (daily freeze-thaw: −3 ℃/5 ℃, 12 h/12 h, 30 times; deep freeze-thaw: −24 ℃/5 ℃, 20 d/10 d, 1 time) using simulated freeze-thaw methods. The changes in soil DOM quantity and quality were investigated based on ultraviolet-visible absorption spectroscopy (UV-vis) and three-dimensional fluorescence spectroscopy combined with parallel factor (EEM-PARAFAC) analysis.
        Result  (1) After 30 d of incubation, the soil dissolved organic carbon (DOC) content was significantly increased. The DOC content of soil samples under day freeze-thaw and deep freeze-thaw conditions was 183.26 and 187.06 mg/kg, respectively, which increased by 18.80% and 21.26% compared with control group (P < 0.05). (2) The UV-vis absorption curves of soil DOM under different freeze-thaw conditions showed little difference, with no obvious characteristic absorption peak, and the absorbance decreased exponentially with the wavelength, but the freeze-thaw samples showed obvious red shift phenomenon. (3) Both freeze-thaw treatments resulted in increased HIX (from 4.42 to 11.73 and 17.10), SUVA254 (from 1.35 mg/(L·cm) to 1.37 and 1.40 mg/(L·cm)) and A253/A203 values (from 0.38 to 0.40 and 0.43) and decreased spectral slope coefficient at wavelength of 275−295 (from 13.34 μm−1 to 13.23 and 12.91 μm−1) of soil DOM. (4) The fluorescent components identified by EEM-PARAFAC included fulvic acid-like substances, humic acid-like substances, soluble microbial metabolites and protein-like substances. Freeze-thaw changed the composition of soil DOM and the percentage of PARAFAC-derived components. The proportions of the three PARAFAC-derived components in the control group were 37%, 32% and 31%, in the daily freeze-thaw group were 41%, 34% and 25% and in the deep freeze-thaw group were 44%, 35% and 21%, respectively.
        Conclusion  Freeze-thaw changes the quantity and quality of DOM in soils, which is manifested in the increase of DOC content and the enhancement of humification degree.

       

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