1米深度林地土壤溶解性有机质垂直分布与光谱特征OA

The forestland soil organic matter is a key support for the global carbon cycle,especially the active carbon component—dissolved organic matter(DOM).The aim of this study is to clarify the total amount,components,and properties of DOM within 1m depth of forestland soil,and to enhance the understanding of the formation,transport,and transformation of DOM in forestland soils.A plantation(main tree species:Koelreuteria paniculata and Cedrus deodara)was selected as a model forestland,and the UV/visible and fluorescence spectroscopy techniques were used to investigate DOM concentrations and their components in the soil layers of 0-20,20-40,40-60,60-80,and 80-100 cm.The results showed that organic carbon and DOM contents in the 0-20 cm soil layer were significantly higher than those in other soil layers,especially than those in the 80-100 cm soil layers,which were 4.1 times higher for TOC and 2.7 times higher for DOC.However,DOC/TOC ratios were relatively high in the 60-80 cm and 80-100 cm soil layers.The UV spectral indices A250/A365,SUVA254,SUVA260,and SR of soil DOM ranged from 4.1 to 20.3,0.3 to 2.6,0.3 to 2.5,and 1.4 to 8.5,respectively.The aromaticity,molecular weight,and hydrophobicity of soil DOM decreased with increasing soil depth.Within the 1m depth,the fluorescence components of soil DOM exhibited distinct vertical differentiation characteristics.Based on parallel factor analysis,five components of soil DOM were identified:two humic-like substances,one fulvic-like substance,one tryptophan-like substance,and one tyrosine-like substance.With increasing soil depth,the contents and proportions of humic-like and fulvic-like substances decreased,with the lowest proportion being 23.7%;in contrast,the content and proportion of tryptophan-like substances increased,reaching up to 53.6%.The FI,BIX,and HIX indices of soil DOM ranged from 1.0 to 1.6,0.6 to 0.9,and 0.4 to 4.7,respectively,indicating that DOM was mainly exogenous such as derived from plant and animal residues.As soil depth increased,the autochthonous characteristics of DOM gradually strengthened,while the humification degree decreased.In conclusion,the results reveal the exogenous characteristics of forestland soil DOM,its stepwise screening and decomposition characteristics along the vertical profile,and the significant heterogeneity of DOM content,components,and properties among different soil layers,these findings provide a data foundation and scientific basis for understanding the underground carbon behavior of forestlands,calculating the underground carbon storage of forestlands,and regulating carbon sequestration in forestlands.