Carbon Dioxide Generation in the Soil-Vadose Continuum: Substrate Characteristics and Residence Times

植物对大气CO2的固定和生物群落对固定碳的矿化（CO2生产）使土壤和大气碳库处于动态平衡状态。最近的水文地质研究表明，CO2的产生也发生在底土渗流区，其对陆地-大气碳平衡的短期和长期影响可能是巨大的。因此，预测土壤C库扰动后果的努力现在必须扩展到底土渗流区。这意味着必须确定对整个土壤-渗流连续体中CO2产生的控制。地下CO2产生的一个关键控制是有机C的可用性，以支持呼吸。在这里，我们将研究的特点和平均停留时间（MRT），这C，以及这些参数如何在两个不同的地质环境下温带草原。在不同深度产生的CO2的14 C年龄的测定将确定现代的，成壤的，和古老的C源，提供估计的MRT的C源的深度变化，从而也提供估计的时间所需的生产在土壤-渗流连续体。我们假设，如果可能的话，以隔离和表征土壤渗流地质材料中的一部分C，可以确定为呼吸基质的碳同位素签名。这种识别将产生新的洞察类型的有机碳作为呼吸底物和它们的演变与深度。它也可以提供方法学基础，使用一个相对简单的隔离程序的基板MRT-深度函数的建设。

Fixation of atmospheric CO2 by plants and mineralization of the fixed C (CO2 production) by respiring biological communities link the soil and atmospheric C reservoirs in a dynamic equilibrium. Resent hydrogeological research has shown that CO2 production also occurs in subsoil vadose zones and that its short-term and long- term impacts on the terrestrial-atmospheric C balance can be substantial. Therefore the effort to predict the consequences of perturbations to the soil C reservoir must now be extended to subsoil vadose zones. This means that controls on CO2 production in the entire soil-vadose continuum must be identified the understood. One key control on subsurface CO2 production is the availability of organic C to support respiration. Here we will study characteristics and mean residence times (MRT) of this C, and how these parameters vary in two contrasting geologic settings beneath temperate grasslands. Determination of the 14C age of the CO2 produced at various depths will identify modern, pedogenic, and ancient C sources, provide estimates of depth variation of MRT of the C sources, and thereby also provide estimates of the time required production in the soil-vadose continuum. We hypothesize that it if possible to isolate and characterize a fraction of C in soil-vadose geologic material which can be identified as respiration substrate by its C isotope signature. Such identification would yield new insight into the types of organic C serving as respiration substrates and their evolution with depth. It may also provide methodological basis for construction of substrate MRT-vs-depth functions using a relatively simple isolation procedure.