植被覆盖下坡面降雨径流对土壤DOM荧光特性的影响

Effect of Rainfall Runoff on DOM Fluorescence of Soil on a Typical Slope Under Vegetation Cover

当前水土流失问题严重,侵蚀环境下土壤生态系统的健康至关重要,而植被覆盖具有固碳保水的作用,利用人工径流设备与人工降雨设备,在6°有无植被种植坡地模拟降雨(暴雨:50 mm·h^(-1)),结合三维荧光光谱技术耦合平行因子法,分析土壤不同坡位径流液中的溶解性有机质(DOM)的来源和组分结构,探究DOM对土壤固碳保水的响应关系。结果表明:(1)与裸地相比,植被覆盖下不同坡位DOM中泥沙含量、可溶性碳(DOC)含量呈现相同的变化趋势:地上径流>壤中流>地下径流;土壤侵蚀量和径流量的变化趋势分别为:壤中流>地下径流>地上径流,地下径流>壤中流>地上径流。(2)根据荧光指数分析,FI与BIX的表征结果基本一致,地上径流DOM来源受内源物代谢影响最大,其次是壤中流,地下径流影响最小,植被覆盖与裸地相比腐殖化来源由内源转变为内源、外源共同作用。腐殖化系数(HIX)与径流液腐殖化程度成正相关关系,植被覆盖下的HIX指数大于裸地的HIX指数,表明径流液腐殖化程度地上径流>壤中流>地下径流,因此植被覆盖可以提高径流液腐殖化程度。(3)平行因子分析表明,不同径流液DOM包括4种荧光组分:类胡敏酸(C1:Ex/Em=260/455 nm)、紫外类富里酸(C2:Ex/Em=240/395 nm)、类色氨酸(C3:Ex/Em=230~275/335,230~275/400 nm)及类酪氨酸(C4:Ex/Em=215/395 nm)。(4)对不同处理荧光强度与F_(max)值分析发现,有植被覆盖处理的F_(max)值均大于裸地,C1、C2和C4组分的F_(max)值变化趋势一致:地上径流>壤中流>地下径流,C3组分的F_(max)值变化趋势:地上径流<壤中流<地下径流。植被覆盖影响土壤中类胡敏酸和类蛋白质物质,对土壤侵蚀起到保护作用,保护幅度:地上径流>壤中流>地下径流。(5)相关分析表明径流量、侵蚀量、泥沙含量相互呈正相关,而C1和C4组分与径流量和侵蚀量呈显著负相关。基于此,根据坡面降雨径流DOM荧光光谱特性,植被覆盖通过改变土壤中的有机质组分,类胡敏酸和类蛋白质物质的稳定性和含量对土壤固土保水有重要作用。

Vegetation covers can do well in carbon sequestration and water retention.In this paper,we used artificial runoff and artificial rainfall equipment to simulate rainfall(storm:50 mm·h^(-1))on a 6°slope with or without vegetation planting.In this case,combined with the 3DEEM-PARAFAC method,the source and component structure of runoff liquid(Dissolved Organic Matter,DOM)at different slope locations are analyzed to determine the relationship between DOM and the carbon and water sequestration effect of the soil.The results showed that:①Compared with bare ground,the reduction of sediment concentration and(Dissolved Organic Carbon,DOC)of the vegetated surface is consistent:overland runoff>through runoff>subsurface runoff.Besides,the rank of the reduction of soil erosion is through runoff>subsurface runoff>overland runoff.Compared with bare ground,the rank of runoff reduction of the vegetated surface is:subsurface runoff>through runoff>overland runoff.②According to the analysis of the fluorescence index,the results of FI and BIX characterization are the same.The source of DOM is influenced by the metabolism of the endogenous material:overland flow>through runoff>subsurface runoff.Compared with the humus source of bare land,the humus source of the vegetated surface changed from endogenous material to the combination of endogenous material and allothigene.The HIX index under vegetation covers is higher than that of bare land,and the degree of humification of runoff fluid is overland flow>through runoff>subsurface runoff.③By parallel factor analysis,different runoff fluid DOM included four fluorescence components:humic acid-like(C1:Ex/Em=260/455 nm),UV fulvic acid-like(C2:Ex/Em=240/395 nm),tryptophan-like(C3:Ex/Em=230~275/335 nm,230~275nm/400 nm)and tyrosine-like(C4:Ex/Em=215/395 nm).④The analysis of fluorescence intensity and Fmax values of different treatments showed that the Fmax values of the treatment with vegetation cover were all greater than those of the bare land.The Fmax values of C1,C2 and C4 components showed the same trend:above-ground runoff>soil flow>underground runoff.The Fmax values of C3 components showed the trend:above-ground runoff<soil flow<underground runoff.Vegetation covers/covered affected the humic acid and protein-like substances in soil,and played a protective role in soil erosion.The protection range was:above-ground runoff>in-soil flow>subsurface runoff.⑤Runoff,erosion,and sediment concentration are positively correlated,while C1 and C4 components are significantly negatively correlated with runoff and erosion.Based on this,according to DOM fluorescence spectrum characteristics of slope rainfall-runoff,vegetation coverage can change organic matter components in soil,which provides the theoretical basis for the healthy development of soil ecosystems in the eroded environment.Moreover,it also indicates that the stability and content of humic acid and protein-like substances play an important role in soil consolidation and water retention.