Soil Cross Institute Programme, North Wyke Research, Okehampton EX20 2SB, UK.
Rapid Commun Mass Spectrom. 2010 Mar 15;24(5):495-500. doi: 10.1002/rcm.4332.
Understanding the fate of dung carbon (C) in soils is challenging due to the ubiquitous presence of the plant-derived organic matter (OM), the source material from which both dung-derived OM and soil organic matter (SOM) predominantly originate. A better understanding of the fate of specific components of this substantial source of OM, and thereby its contribution to C cycling in terrestrial ecosystems, can only be achieved through the use of labelled dung treatments. In this short review, we consider analytical approaches using bulk and compound-specific stable carbon isotope analysis that have been utilised to explore the fate of dung-derived C in soils. Bulk stable carbon isotope analyses are now used routinely to explore OM matter cycling in soils, and have shown that up to 20% of applied dung C may be incorporated into the surface soil horizons several weeks after application, with up to 8% remaining in the soil profile after one year. However, whole soil delta(13)C values represent the average of a wide range of organic components with varying delta(13)C values and mean residence times in soils. Several stable (13)C isotope ratio mass spectrometric methods have been developed to qualify and quantify different fractions of OM in soils and other complex matrices. In particular, thermogravimetry-differential scanning calorimetry-isotope ratio mass spectrometry (TG-DSC-IRMS) and gas chromatography-combustion-IRMS (GC-C-IRMS) analyses have been applied to determine the incorporation and turnover of polymeric plant cell wall materials from C(4) dung into C(3) grassland soils using natural abundance (13)C isotope labelling. Both approaches showed that fluxes of C derived from polysaccharides, i.e. as cellulose or monosaccharide components, were more similar to the behaviour of bulk dung C in soil than lignin. However, lignin and its 4-hydroxypropanoid monomers were unexpectedly dynamic in soil. These findings provide further evidence for emerging themes in biogeochemical investigations of soil OM dynamics that challenge perceived concepts of recalcitrance of C pools in soils, which may have profound implications for the assessment of the potential of agricultural soils to influence terrestrial C sinks.
理解粪便碳（C）在土壤中的命运具有挑战性，因为植物衍生的有机质（OM）无处不在，而粪便衍生的 OM 和土壤有机质（SOM）主要来源于这种源材料。只有通过使用标记粪便处理，才能更好地了解这种大量 OM 源的特定成分的命运，从而了解其对陆地生态系统碳循环的贡献。在这篇简短的综述中，我们考虑了使用批量和化合物特异性稳定碳同位素分析来探索粪便衍生 C 在土壤中命运的分析方法。批量稳定碳同位素分析现在已被常规用于探索土壤中 OM 物质循环，并表明在施用后数周内，高达 20%的应用粪便 C 可能被纳入表层土壤，在一年后仍有高达 8%的粪便 C 留在土壤剖面中。然而，整个土壤 delta(13)C 值代表了具有不同 delta(13)C 值和在土壤中平均停留时间的各种有机成分的平均值。已经开发了几种稳定（13)C 同位素比质谱方法来定性和定量土壤和其他复杂基质中的不同 OM 分数。特别是，热重-差示扫描量热法-同位素比质谱（TG-DSC-IRMS）和气相色谱-燃烧-IRMS（GC-C-IRMS）分析已被应用于使用自然丰度（13)C 同位素标记确定 C(4)粪便中聚合物植物细胞壁材料向 C(3)草地土壤中的掺入和周转。这两种方法都表明，源自多糖的 C 通量，即作为纤维素或单糖成分，在土壤中比木质素更类似于批量粪便 C 的行为。然而，木质素及其 4-羟基丙基单体在土壤中出乎意料地具有动态性。这些发现为土壤 OM 动态生物地球化学研究中出现的主题提供了进一步的证据，这些主题挑战了土壤中 C 库的抗降解性的概念，这可能对评估农业土壤影响陆地 C 汇的潜力具有深远的影响。
