水土保持林恢复土壤可溶性碳氮组分动态与三维荧光特征分析

Analysis of dynamics of soil dissolved carbon and nitrogen fractions and its three-dimensional fluorescence characteristics during restoration of soil and water conservation forests

为探究水土保持林恢复过程中土壤可溶性碳氮含量变化及其有机组成特性,揭示水保林土壤固存可溶性有机质的效应及机制。选取了黄土丘陵区恢复12—45a的人工柠条、刺槐林以及撂荒地,分析了土壤可溶性碳氮含量及其三维荧光光谱特征与特性参数的动态变化。结果表明:随恢复年限的增加,3种植被土壤可溶性有机碳(DOC)、有机氮(DON)、无机氮(DIN)的含量均呈增加趋势,并且相同恢复年限下DOC、DON、DIN含量总体表现为撂荒<柠条<刺槐;但柠条和刺槐林土壤DOC:DON及二者占总有机碳、全氮比例并未持续增加,到恢复45a时DOC占总有机碳比例以及DOC:DON均以撂荒地最高,刺槐林最低,DON占全氮比例则表现相反。三维荧光结合平行因子分析得出所有样地土壤可溶性有机质(DOM)主要有大分子腐殖物质(C1)、低分子量类富里酸(C2)、类色氨酸(C3)及农业措施输入的腐殖物质(C4)4个组分,并且以C1组分占比最大,平均达37.4%。随恢复年限增加,3种植被土壤DOM中C3组分占比升高,C2和C4组分占比降低,C1组分占比在柠条和刺槐林中升高,在撂荒地中则降低。不同植被土壤可溶性有机质荧光指数(FI)、新鲜度指数(β:α)及自生源指数(BIX)差异不显著,分别为1.63、0.58、0.59;不同恢复年限撂荒地腐殖化指数(HIX)没有差异,但柠条和刺槐林显著高于撂荒且随恢复年限增加先增大后稳定。综上,水保林持续恢复可以显著提升土壤可溶性碳氮含量,也使土壤可溶有机质组成趋向复杂和相对稳定,利于累积固持,特别以刺槐林效应最明显。

For revealing the effects and mechanism of dissolved organic matter(DOM)accumulation in soil during the restoration process of soil and water conservation forests,the dynamics of dissolved carbon and nitrogen content and its organic composition characteristics was analyzed in the surface soil.The soils were collected from three typical kinds of forestlands:Caragana korshinskii,Robinia pseudoacacia and abandoned land,which have been established for 12 to 45 years,and changes in soil dissolved carbon and nitrogen content,three-dimensional fluorescence characteristics and parameters were determined.The results showed that the contents of dissolved organic carbon(DOC),dissolved organic nitrogen(DON)and dissolved inorganic nitrogen(DIN)in the three vegetation soils increased significantly with recovery duration.Under the same recovery period,the contents of DOC,DON and DIN generally appear as abandoned land<Caragana korshinskii<Robinia pseudoacacia.However,the ratios of DOC to SOC,DON to TN and DOC to DON in Caragana korshinskii and Robinia pseudoacacia did not increase continuously.After 45 years,the ratio of DOC to SOC and DOC to DON were the highest in abandoned land and the lowest in Robinia pseudoacacia.The ratio of DON to TN was the highest in Robinia pseudoacacia,while the lowest in abandoned land.Three-dimensional fluorescence spectroscopy combined with parallel factor(EEM-PARAFAC)analysis showed that the dissolved organic matter(DOM)in all plots mainly consists of 4 components:macromolecule humus(C1),fulvic acid(C2),tryptophan-like(C3),and humus substance related to human activities such as manure(C4).The C1 component has the largest proportion,with an average proportion of 37.4%.With the extension of the restoration period,the proportion of C3 component in soil DOM of the three vegetation types increased,the proportion of C2 and C4 components decreased,the proportion of C1 component increased in Caragana korshinskii and Robinia pseudoacacia forests and decreased in abandoned land.The DOM fluorescence index(FI),freshness index(β:α),and biological index(BIX)of all plots were not significantly different.The average fluorescence index of each plot was 1.63,the average freshness index was 0.58,and the biological index was 0.59.The humification index(HIX)of abandoned land at different restoration years has no difference.The humification index of Caragana korshinskii and Robinia pseudoacacia forests are significantly higher than the abandoned land.The humification index of Caragana korshinskii forest restored 45 years and 28 years was significantly higher than that of restoration 18a,and the humification index of Robinia pseudoacacia forest restored 45 years and 18 years was significantly higher than 12 years.In conclusion,the continuous restoration of soil and water conservation forests significantly increased the content of soil dissolved carbon and nitrogen,and result in more stable and complex composition of dissolved organic matter,which is conducive to continuous accumulation,especially in the Robinia pseudoacacia forestland.