Deep soil organic matter-a key but poorly understood component of terrestrial C cycle
Deep soil organic matter-a key but poorly understood component of terrestrial C cycle
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DOI：
10.1007/s11104-010-0391-5
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发表时间：
2011-01-01
期刊：
影响因子：
4.9
通讯作者：
Koegel-Knabner, Ingrid
中科院分区：
文献类型：
--
作者：
Rumpel, Cornelia;Koegel-Knabner, Ingrid
尽管碳 (C) 含量较低，但大多数底土层的碳储量占土壤总碳储量的一半以上，因此需要在全球碳循环中予以考虑。直到最近，深层土壤中碳的性质和动态在很大程度上被忽视。本综述的目的是综合有关地下层土壤有机质 (SOM) 的来源、组成、稳定和失稳机制的文献。输入到底土中的有机碳以溶解形式 (DOC) 遵循优先流动路径，如地上或根部凋落物以及沿着根通道和/或通过生物扰动的渗出物。这些输入对于底土碳分布和动态的相对重要性仍需要评估。一般来说，深层土壤层中的碳的特点是平均停留时间长达数千年。除少数例外，碳氮（C/N）比随着土壤深度的增加而减小，而SOM的稳定C和N同位素比则增加，表明深层土壤层中的有机质（OM）被高度加工。多项研究表明，与表土 SOM 相比，底土中的 SOM 富含微生物来源的 C 化合物，但富含能量的植物物质却较少。然而，底土中 SOM 的化学成分因土壤类型而异，并且受土壤过程的影响很大。据报道，与矿物相，特别是非晶态铁（Fe）和铝（Al）氧化物的相互作用是酸性和近中性土壤中的主要稳定机制。此外，土壤团聚体内的吸藏已被确定为保存在底土中的 SOM 的很大一部分。实验室研究表明，添加不稳定的碳可以刺激具有高停留时间的底土碳的分解。导致底土中 SOM 不稳定的其他机制包括破坏土壤微生物的物理结构和养分供应。导致底土中 SOM 受到保护的最重要因素之一可能是 SOM、微生物和细胞外酶活性的空间分离，这可能与 C 输入的异质性有关。由于不同的过程，底土中的稳定 SOM 呈水平分层。为了更好地了解深层 SOM 动力学并将其纳入土壤 C 模型中，需要有关现场尺度的 C 输入、稳定和不稳定过程产生的 C 通量的定量信息。
Despite their low carbon (C) content, most subsoil horizons contribute to more than half of the total soil C stocks, and therefore need to be considered in the global C cycle. Until recently, the properties and dynamics of C in deep soils was largely ignored. The aim of this review is to synthesize literature concerning the sources, composition, mechanisms of stabilisation and destabilization of soil organic matter (SOM) stored in subsoil horizons. Organic C input into subsoils occurs in dissolved form (DOC) following preferential flow pathways, as aboveground or root litter and exudates along root channels and/or through bioturbation. The relative importance of these inputs for subsoil C distribution and dynamics still needs to be evaluated. Generally, C in deep soil horizons is characterized by high mean residence times of up to several thousand years. With few exceptions, the carbon-to-nitrogen (C/N) ratio is decreasing with soil depth, while the stable C and N isotope ratios of SOM are increasing, indicating that organic matter (OM) in deep soil horizons is highly processed. Several studies suggest that SOM in subsoils is enriched in microbial-derived C compounds and depleted in energy-rich plant material compared to topsoil SOM. However, the chemical composition of SOM in subsoils is soil-type specific and greatly influenced by pedological processes. Interaction with the mineral phase, in particular amorphous iron (Fe) and aluminum (Al) oxides was reported to be the main stabilization mechanism in acid and near neutral soils. In addition, occlusion within soil aggregates has been identified to account for a great proportion of SOM preserved in subsoils. Laboratory studies have shown that the decomposition of subsoil C with high residence times could be stimulated by addition of labile C. Other mechanisms leading to destabilisation of SOM in subsoils include disruption of the physical structure and nutrient supply to soil microorganisms. One of the most important factors leading to protection of SOM in subsoils may be the spatial separation of SOM, microorganisms and extracellular enzyme activity possibly related to the heterogeneity of C input. As a result of the different processes, stabilized SOM in subsoils is horizontally stratified. In order to better understand deep SOM dynamics and to include them into soil C models, quantitative information about C fluxes resulting from C input, stabilization and destabilization processes at the field scale are necessary.