Sources and degradability of organic matter revealed by 14C analysis

在全球陆地碳库中，地下有机质被认为是一个巨大的有机碳储量，需要考虑。到目前为止，人们对底土的组成和动态还不太了解，并且仍然不清楚是哪些过程控制了放射性碳年龄随土壤深度的强烈增长。因此，研究单位1806使用了一套广泛的方法来确定导致地下土壤中有机碳积累和稳定的机制。该子项目利用放射性碳和有机地球化学分析来区分地下层位的不同有机来源，并确定其可降解性。在第一个项目阶段，我们确定了根系分布与有机碳含量及其放射性碳年龄的密切相关性。然而，根系的丰度-新鲜有机碳的主要来源-随着土壤深度的增加而显著下降。地下层位的放射性碳含量高达9000年BP，表明非常古老的潜在地源碳对土壤深度的贡献很大且不断增加。相比之下，从几百到几千年前的地下土层中呼出的二氧化碳具有现代放射性碳含量，这表明存在新鲜/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物组分，b)更详细地评估底土中有机物的可降解性。我们将分析不同的难降解有机碳库，建立并应用新的方法来测定地下层和微生物膜脂中的放射性碳年代二氧化碳。这将为我们提供有关底土中稳定和不稳定有机基质及其可降解性的信息。

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.