Soil organic matter (SOM) plays an essential role in agronomic systems and is of great importance to environmental sustainability and carbon sequestration. This study evaluates the accumulation of carbon in soils from integrated agricultural systems (S) that include crop (C), livestock (L), and forest (F) components (in different combinations: CLFS, LFS and CLS) and an undisturbed native forest (NF) as a reference area. The study sites are part of the Embrapa Pecuária Sudeste research station located in the southeast of Brazil in a region of dystrophic Red-Yellow Latosol soils. Stable carbon isotopic analysis (δ¹³C) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopy were used to evaluate the chemical characteristics of humic acid (HA) extracts of soils from different soil horizons. The findings were discussed in the context of laser-induced fluorescence spectroscopy (LIFS) measurements on the whole soils and carbon content on both the whole soils and HA extracts. With increasing depth of the soil horizons, bulk SOM (in the whole soil) and a more recalcitrant humic fraction (the HA) became enriched in carbon, indicative of accumulation. Isotopic analysis revealed that SOM in the crop-livestock-forest system exhibited δ¹³C signatures corresponding to C4 plants (grass and corn). The native forest exhibited a uniform δ¹³C signature characteristic of C3 plants (native trees). Benzenepolycarboxylic acids (BPCA) quantification on limited samples revealed condensed aromatic structures in both crop-livestock-forest system and native forest. The absence of burning suggests that these compounds come from the humification of lignin. Based on structural characterization, carbon is sequestered as recalcitrant and long-lived oxidized ligninaceous structures and condensed aromatic groups. The current research demonstrates the feasibility of novel agricultural approaches such as using crop-livestock-forest systems. Such pastureland management enhances higher agricultural productivity and sustainability, thus avoiding new deforestation of native areas.

中文翻译：

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巴西东南部综合农业系统土壤有机质化学特征

土壤有机质 (SOM) 在农艺系统中起着至关重要的作用，对环境可持续性和碳封存具有重要意义。本研究评估了综合农业系统 (S) 土壤中碳的积累，包括作物 (C)、牲畜 (L) 和森林 (F) 成分（不同组合：CLFS、LFS 和 CLS）和未受干扰的原生森林(NF) 作为参考区域。这些研究地点是Embrapa Pecuária Sudeste研究站的一部分，该研究站位于巴西东南部的一个营养不良的红黄色拉托索土壤地区。稳定碳同位素分析 (δ ¹³ C) 和固态¹³ C 核磁共振 ( ¹³C NMR）光谱用于评估来自不同土壤层的土壤的腐殖酸（HA）提取物的化学特性。在对整个土壤和整个土壤和 HA 提取物的碳含量进行激光诱导荧光光谱 (LIFS) 测量的背景下讨论了这些发现。随着土壤层深度的增加，大量 SOM（在整个土壤中）和更顽固的腐殖质部分（HA）变得富含碳，表明积累。同位素分析表明，作物-牲畜-森林系统中的 SOM 表现出与 C4 植物（草和玉米）相对应的 δ ¹³ C 特征。原生林呈现出均匀的 δ ¹³C3 植物（原生树木）的 C 特征。对有限样本的苯多羧酸 (BPCA) 定量揭示了作物-牲畜-森林系统和原生森林中的稠合芳香结构。没有燃烧表明这些化合物来自木质素的腐殖化。基于结构表征，碳被隔离为顽固和长寿命的氧化木质结构和稠合芳香基团。目前的研究证明了新农业方法的可行性，例如使用作物-牲畜-森林系统。这种牧场管理提高了农业生产力和可持续性，从而避免了对原生地区的新森林砍伐。