基于3DEEM-PARAFAC的短期稻虾共作土壤DOM荧光光谱分析

Fluorescence spectrometric analysis of dissolved organic matter(DOM)in soil from a short-term integrated rice-crayfish system based on 3DEEM-PARAFAC

稻虾共作模式已在中国长江中下游地区广泛应用。为研究短期稻虾共作对土壤溶解性有机物(DOM)组成和腐殖化的影响,采用三维荧光光谱耦合平行因子法(3DEEM-PARAFAC)分析土壤DOM荧光组分和各组分变化规律,利用腐殖化指数(HIX)、腐殖酸与色氨酸荧光比值(A∶T)、新鲜指数(β:α)、McKnight荧光指数(MFI)、Y型荧光指数(YFI)等多种荧光光谱指数表征DOM腐殖化程度,并通过皮尔逊相关系数进行相关性分析。研究发现,土壤DOM包括3个荧光组分,C1为较低相对分子质量的腐殖质类物质,C2为较高芳香度的UVC类腐殖质,C3为酪氨酸类物质,未发现高相对分子质量腐殖质类物质。在0~20.0 cm表层土壤中,C1、C2组分荧光强度随采样时间的推迟呈先上升后下降趋势,峰值出现在水稻分蘖期或抽穗期,而C3组分荧光强度无明显变化规律。皮尔逊相关系数分析结果显示,腐殖质类物质C1荧光强度与C2荧光强度呈显著正相关性(r=0.99,P<0.001),蛋白质类物质C3荧光强度与其他荧光指数(强度)相关性均较弱(r<0.40)。HIX与C1荧光强度、A∶T呈显著正相关,均可被线性函数拟合。相较于MFI,YFI更能反映土壤中DOM的腐殖化变化特性,YFI与HIX可被指数函数较好拟合。研究认为,短期稻虾共作土壤的腐殖化特征主要受内源有机质降解影响,而受外源蛋白质类物质输入的影响较小,且难以通过分析溶解性有机碳含量来监测土壤有机质腐殖化程度。

Integrated rice-crayfish system has been widely used in the middle and lower reaches of Yangtze River in China.To study the effects of short-term integrated rice-crayfish system on composition and humification of dissolved organic matter(DOM)from the soil,three-dimensional excitation emission matrix fluorescence spectroscopy coupled parallel factor method(3DEEM-PARAFAC)was used to analyze the fluorescence components and the changes of each component of soil DOM.Different fluorescence spectrum indexes including humification index(HIX),ratio of humic acid fluoescence intensity to tryptophan fluorescence intensity(A∶T),freshness index(β∶α),McKnight fluorescence index(MFI),Y-type fluorescence index(YFI)were used to characterize the degree of DOM humification.Pearson correlation coefficient was used to analyze the correlation.The results showed that three fluorescence components were identified from soil DOM,containing humic substances with low relative molecular weight(C1),UVC humic substances with high aromatic degree(C2)and tyrosine-like substances(C3),no humic substance with relative high molecular weight was found.In the surface soil of 0-20.0 cm depht,the fluorescence intensity of C1 and C2 components increased firstly and then decreased as the sampling time pastponed,the highest value appeared at the tillering or heading stage of rice,while no definite trend was found for the C3 component.Pearson correlation coefficient analysis demonstrated that the fluorescence intensity of humic substances C1 and C2 showed significant positive correlation(r=0.99,P<0.001);the fluorescence intensity of protein substance C3 had weak relationship with other fluorescence indices(intensities)(r<0.40).HIX showed significant positive correlation with the fluorescence intensity of C1 and A∶T,which could be fitted by a linear function.Compared with MFI,YFI had sufcient distinguishing capacity to characterize the humification process of DOM in the soil;YFI and HIX could be fitted well by an exponential function.It can be concluded from the study that the humification characteristics of the soil in the short-term integrated rice-crayfish system are mainly affected by the degradation of endogenous organic matter,but are less affected by the input of exogenous protein substances.It is hard to monitor the humification degree of soil organic matter by analyzing dissolved organic carbon content of the soil.