Sierra Carlos A, Hoyt Alison M, He Yujie, Trumbore Susan E
Max Planck Institute for Biogeochemistry Jena Germany.
Department of Earth System Science University of California Irvine CA USA.
Global Biogeochem Cycles. 2018 Oct;32(10):1574-1588. doi: 10.1029/2018GB005950. Epub 2018 Oct 26.
The question of why some types of organic matter are more persistent while others decompose quickly in soils has motivated a large amount of research in recent years. Persistence is commonly characterized as turnover or mean residence time of soil organic matter (SOM). However, turnover and residence times are ambiguous measures of persistence, because they could represent the concept of either age or transit time. To disambiguate these concepts and propose a metric to assess SOM persistence, we calculated age and transit time distributions for a wide range of soil organic carbon models. Furthermore, we show how age and transit time distributions can be obtained from a stochastic approach that takes a deterministic model of mass transfers among different pools and creates an equivalent stochastic model at the level of atoms. Using this approach we show the following: (1) Age distributions have relatively old mean values and long tails in relation to transit time distributions, suggesting that carbon stored in soils is on average much older than carbon in the release flux. (2) The difference between mean ages and mean transit times is large, with estimates of soil organic carbon persistence on the order of centuries or millennia when assessed using ages and on the order of decades when using transit or turnover times. (3) The age distribution is an appropriate metric to characterize persistence of SOM. An important implication of our analysis is that random chance is a factor that helps to explain why some organic matter persists for millennia in soil.
近年来，为何某些类型的有机物质在土壤中更持久，而其他有机物质却迅速分解，这一问题引发了大量研究。持久性通常被表征为土壤有机质（SOM）的周转或平均停留时间。然而，周转和停留时间是持久性的模糊度量，因为它们可能代表年龄或转运时间的概念。为了明确这些概念并提出一种评估SOM持久性的指标，我们计算了一系列土壤有机碳模型的年龄和转运时间分布。此外，我们展示了如何从一种随机方法中获得年龄和转运时间分布，该方法采用不同库之间质量转移的确定性模型，并在原子水平上创建一个等效的随机模型。使用这种方法，我们展示了以下内容：（1）与转运时间分布相比，年龄分布具有相对较老的平均值和长尾，这表明土壤中储存的碳平均比释放通量中的碳要老得多。（2）平均年龄和平均转运时间之间的差异很大，当使用年龄评估时，土壤有机碳持久性的估计值在几个世纪或几千年的量级，而使用转运或周转时间时则在几十年的量级。（3）年龄分布是表征SOM持久性的合适指标。我们分析的一个重要含义是，随机因素有助于解释为什么有些有机物质在土壤中能持续存在数千年。
