Research on the Effects of Aging Microplastics on Soil Nitrogen and Dissolved Organic Matter in Dryland Soil

微塑料是一种新型污染物，土壤是微塑料在陆地生态系统中的主要汇，但微塑料对土壤生态系统的影响尚未完全明确。为探究微塑料对农田土壤中氮素及溶解性有机物(DOM)的影响机制，本研究以淮南市旱地农田耕地土壤为研究对象，利用紫外光谱和三维荧光光谱表征土壤DOM，探究不同老化程度的微塑料在旱地土壤中的积累对土壤氮素和DOM的影响。结果表明：1) 微塑料的添加会导致旱地土壤中氨氮、硝态氮及全氮含量下降，且其老化程度和含量对氮素含量变化速率产生影响。2) 紫外光谱分析显示，微塑料的添加增加了旱地土壤DOM对紫外光的吸收，降低了其腐殖化程度。同时，微塑料进入土壤后，土壤疏水性有机组分的含量减少，且其变化与微塑料老化相关。3) 微塑料的添加导致土壤DOM中UVC腐殖质、陆生腐殖质样组分以及蛋白质样组分的减少，而蛋白质中色氨酸样组分的含量增加。因此，微塑料不仅通过改变旱地土壤中氮素的含量影响土壤氮循环，还改变DOM的组分比例，进而影响土壤有机质的质量和稳定性。Microplastics are emerging contaminants, and soil serves as the primary sink for microplastics in terrestrial ecosystems. However, the impacts of microplastics on soil ecosystems remain incompletely understood. In order to explore the influence mechanism of microplastics on nitrogen and dissolved organic matter (DOM) in farmland soil, this study took the farmland soil of dry farmland in Huainan City as the research object, and used ultraviolet spectrum and three-dimensional fluorescence spectrum to characterize soil DOM, and explored the effects of the accumulation of microplastics in dry farmland soil with different aging degrees on soil nitrogen and DOM. The results showed that: 1) The addition of microplastics would lead to a decrease in ammonia nitrogen, nitrate nitrogen and total nitrogen content in dryland soil, and its aging degree and content would affect the change rate of nitrogen content. 2) UV spectrum analysis showed that the addition of microplastics increased the absorption of ultraviolet light by DOM in dryland soil and reduced its humification degree. At the same time, after microplastics enter the soil, the content of soil hydrophobic organic components decreases, and this change is related to the aging of microplastics. 3) The addition of microplastics led to the decrease of UVC humus, terrestrial humus-like components and protein-like components in soil DOM, while the content of tryptophan-like components in protein increased. Therefore, microplastics not only affect soil nitrogen cycle by changing the content of nitrogen in dryland soil, but also change the proportion of DOM components, thus affecting the quality and stability of soil organic matter.