College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, PR China.
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, PR China.
Sci Total Environ. 2019 Nov 20;692:613-621. doi: 10.1016/j.scitotenv.2019.07.339. Epub 2019 Jul 22.
Dissolved organic matter (DOM) is a natural chemical component of all soils and influences soil organic pollutant migration, nutrient cycling, and global climate change. Previous field studies have focused on a single ecosystem, such as cropland, grassland, or forestland. However, the potential effect of different land-use types on the vertical distribution of soil DOM quantity and quality remains unclear. This study investigated the vertical characteristics of DOM in 5-m soil profiles under different land-use types (cropland, grassland, and forestland) on the Loess Plateau. The data from ultraviolet-visible spectral and parallel factor analysis of fluorescence excitation-emission matrix spectrophotometry were combined. These results indicated that the mean content of dissolved organic carbon (DOC) in the 30-yr forestland (203.33 mg kg soil) was the highest, and the lowest was observed in the cropland (83.70 mg kg soil). Meanwhile, the mean DOC content of the forestland increased through time, particularly after 20 years. In other words, afforestation activities only significantly affected soil DOM after a long time (over 20 years). The DOC content of the cropland initially increased and then decreased with soil depth in the 1-m soil profiles, which may be related to agricultural activities. Three fluorescence components, including two humic acid-like substances (C1 and C3) and a tryptophan-like substance (C2), were identified from all samples. The humic acid-like components significantly decreased by 51% with soil depth, while the tryptophan-like component increased by 49%, particularly in the cropland. The variation in ultraviolet-visible spectral and optical indexes also indicated that soil DOM was dominated by both microbial and terrestrial sources. These findings help to understand the dynamics of DOC in deep soil profiles and the biogeochemical effects of DOM in the natural environment.
溶解有机物质（DOM）是所有土壤的天然化学成分，它影响土壤有机污染物的迁移、养分循环和全球气候变化。以前的实地研究集中在单一生态系统，如农田、草地或林地。然而，不同土地利用类型对土壤 DOM 数量和质量垂直分布的潜在影响仍不清楚。本研究调查了黄土高原不同土地利用类型（农田、草地和林地）下 5m 土壤剖面中 DOM 的垂直特征。将紫外可见光谱和荧光激发-发射矩阵分光光度法平行因子分析的数据结合起来。结果表明，30 年林地（203.33mgkg土壤）中溶解有机碳（DOC）的平均含量最高，农田（83.70mgkg土壤）中最低。同时，林地的 DOC 含量随着时间的推移而增加，特别是在 20 年以后。换句话说，造林活动只有在很长一段时间（20 年以上）后才会显著影响土壤 DOM。农田 1m 土壤剖面中 DOC 含量随土壤深度先增加后减少，这可能与农业活动有关。从所有样本中鉴定出三种荧光成分，包括两种腐殖酸类物质（C1 和 C3）和一种色氨酸类物质（C2）。腐殖酸类物质随土壤深度显著减少 51%，而色氨酸类物质增加 49%，特别是在农田中。紫外可见光谱和光学指标的变化也表明，土壤 DOM 主要来源于微生物和陆地来源。这些发现有助于了解深层土壤剖面中 DOC 的动态变化以及 DOM 在自然环境中的生物地球化学效应。
