The subtropical zone in China is one of the regions most affected by nitrogen deposition. Soil dissolved organic matter (DOM) is considered to be an important indicator of soil organic matter. Nitrogen deposition may alter the quality and quantity of soil DOM by changing soil microbial activity. In this study, we explored the effects of nitrogen addition on soil DOM content, its spectral characteristics and microbial extraceller enzyme activity in the Moso bamboo plantations by setting control (CT), low-nitrogen (LN), and high-nitrogen (HN) addition levels for three-year nitrogen addition. The results showed that there was no significant change in soil pH, dissolved organic carbon, dissolved organic nitrogen, and aroma index following nitrogen addition, while the humification index increased significantly, microbial enzyme activities increased first and then decreased with the increases of nitrogen addition. Fourier transform infrared spectroscopy results showed that soil DOM had similar absorption peaks in seven regions, and that the absorption peaks of 1000 to 1260 cm-1 were the strongest, indicating an enhanced amount of polysaccharides, alcohols, carboxyl acids, and esters after nitrogen addition. The results of three-dimensional fluorescence spectroscopy showed that soil DOM structure significantly changed following nitrogen addition, with a decrease in low-molecular substances such as protein-like substances and microbial metabolites and a significant increase in high-molecular substances such as humus-like substances. In general, nitrogen addition made soil nitrogen compatible with microbial requirements. Microorganisms decompose substances that were easily degraded in DOM. The structure of soil DOM was more complex after nitrogen addition. Therefore, short-term nitrogen deposition might be conducive to preserving soil fertility.
中国亚热带是受氮沉降影响最严重的地区之一.土壤可溶性有机质(DOM)被认为是土壤有机质的重要指标,氮沉降可能通过改变微生物活性导致土壤DOM质量和数量的变化.本研究以亚热带毛竹林为研究对象,设置对照、低氮和高氮3个水平,进行为期3年的施氮处理,探究氮添加对土壤DOM含量、光谱学特征和微生物胞外酶活性的影响.结果表明: 与对照相比,施氮后土壤pH、可溶性有机碳、可溶性有机氮含量和芳香化指数无显著变化,而腐殖化指数随施氮量的增加显著增加,微生物酶活性也随着施氮量的增加呈现先升高后下降的趋势.傅里叶红外光谱结果显示,土壤DOM在7个区域的相似位置存在吸收峰,其中,1000～1260 cm-1的吸收峰最强,表明施氮处理后,土壤中多糖类、醇类、羧酸类及酯类物质增加.三维荧光光谱结果表明,施氮处理后,土壤DOM结构有显著改变,表现在低分子物质如类蛋白质物质和微生物代谢产物减少,而高分子物质如类腐殖质物质显著增加.总的来说,施氮使得土壤氮与微生物需求相适应,促进微生物分解DOM中易降解的物质,土壤DOM结构更加复杂,短期氮沉降可能有利于土壤肥力的改善.
Keywords: enzyme activity; nitrogen deposition; soil dissolved organic matter (DOM); three-dimensional fluorescence spectra.