Sources and degradability of organic matter revealed by 14C analysis

储存在底土中的有机质被认为是全球陆地有机碳库中需要考虑的一个大的有机碳库。到目前为止，下层土壤的组成和动力学还不是很清楚，也不清楚是什么过程控制了放射性碳年龄随土壤深度的强劲增长。因此，研究单位1806使用一套广泛的方法来确定导致有机碳在底土中积累和稳定的机制。这一分项目使用放射性碳和有机地球化学分析来区分地下土层中的不同有机来源，并确定它们的降解性。在第一个项目阶段，我们确定了根的分布与有机碳量及其放射性碳年龄密切相关。然而，根的丰度--底层土壤新鲜有机碳的主要来源--随着土壤深度的增加而显著减少。底土层的放射性碳含量高达9000年BP，这表明随着土壤深度的增加，非常古老的潜在地源碳的贡献越来越大。相比之下，从几百年到几千年的地下土层呼吸的二氧化碳具有现代放射性碳含量，这表明存在新的/年轻的有机化合物，并优先被降解。在这个项目的第二阶段，我们的目标是a)识别和表征旧的有机质组分，b)更详细地评估底土中有机质的降解性。我们将分析不同的难处理有机碳库，并建立和应用新的方法来测定地下土层中的二氧化碳和微生物膜脂的放射性碳数据。这将为我们提供有关底土中稳定和不稳定的有机底物及其降解性的信息。

The organic matter stored in subsoils has been recognized as a large organic carbon stock that needs to be considered in the global terrestrial OC pool. Until now the composition and dynamics of subsoil are not well understood and it remains unclear, which processes control the strong increase in the radiocarbon age with soil depth. The research unit 1806 thus uses a broad set of methods to identify mechanisms leading to the accumulation and stabilization of organic carbon in subsoils. This subproject uses radiocarbon and organic-geochemical analyses to differentiate different organic sources in subsoil horizons and to determine their degradability. During the first project phase we determined a close correlation of the distribution of roots with the amount of organic carbon and its radiocarbon age. However, the abundance of roots - the major source of fresh organic carbon to subsoils - decreased considerably with soil depth. Radiocarbon contents of subsoil horizon were up to 9000 years BP suggesting a large and increasing contribution of very old, potentially geogenic carbon with soil depth. In contrast, the carbon dioxide respired from several hundred to thousand year old subsoil horizons had modern radiocarbon contents suggesting that fresh/young organic compounds are present and are degraded preferentially. During the second phase of this project our aim is to a) identify and characterize the old organic matter fraction and b) to evaluate the degradability of organic matter in subsoils in more detail. We will analyse different refractory organic carbon pools and establish and apply novel methods to radiocarbon date CO2 in subsoil horizons and microbial membrane lipids. This will give us information on stable and labile organic substrates in subsoils and their degradability.