Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration, ECNU-UH Joint Translational Science and Technology Research Institute, School of Ecological and Environmental Sciences, East China Normal University, Shanghai, China.
Center for Global Change and Ecological Forecast, East China Normal University, Shanghai, China.
Glob Chang Biol. 2018 Feb;24(2):810-822. doi: 10.1111/gcb.13994. Epub 2018 Jan 3.
Temperature sensitivity of soil organic carbon (SOC) decomposition is one of the major uncertainties in predicting climate-carbon (C) cycle feedback. Results from previous studies are highly contradictory with old soil C decomposition being more, similarly, or less sensitive to temperature than decomposition of young fractions. The contradictory results are partly from difficulties in distinguishing old from young SOC and their changes over time in the experiments with or without isotopic techniques. In this study, we have conducted a long-term field incubation experiment with deep soil collars (0-70 cm in depth, 10 cm in diameter of PVC tubes) for excluding root C input to examine apparent temperature sensitivity of SOC decomposition under ambient and warming treatments from 2002 to 2008. The data from the experiment were infused into a multi-pool soil C model to estimate intrinsic temperature sensitivity of SOC decomposition and C residence times of three SOC fractions (i.e., active, slow, and passive) using a data assimilation (DA) technique. As active SOC with the short C residence time was progressively depleted in the deep soil collars under both ambient and warming treatments, the residences times of the whole SOC became longer over time. Concomitantly, the estimated apparent and intrinsic temperature sensitivity of SOC decomposition also became gradually higher over time as more than 50% of active SOC was depleted. Thus, the temperature sensitivity of soil C decomposition in deep soil collars was positively correlated with the mean C residence times. However, the regression slope of the temperature sensitivity against the residence time was lower under the warming treatment than under ambient temperature, indicating that other processes also regulated temperature sensitivity of SOC decomposition. These results indicate that old SOC decomposition is more sensitive to temperature than young components, making the old C more vulnerable to future warmer climate.
土壤有机碳（SOC）分解的温度敏感性是预测气候-碳（C）循环反馈的主要不确定因素之一。先前研究的结果存在很大的矛盾，即旧土壤 C 的分解比年轻部分更敏感、相似或对温度不敏感。这些矛盾的结果部分来自于在没有或有同位素技术的实验中，区分旧和年轻 SOC 及其随时间变化的困难。在这项研究中，我们进行了一项长期的野外培养实验，使用深土套（0-70 厘米深，10 厘米直径的 PVC 管）排除根 C 输入，以检查 2002 年至 2008 年在环境和增温处理下 SOC 分解的表观温度敏感性。该实验的数据被注入到一个多池土壤 C 模型中，使用数据同化（DA）技术估计 SOC 分解的固有温度敏感性和三个 SOC 分数（即活跃、缓慢和被动）的 C 居留时间。由于活跃 SOC 的 C 居留时间较短，在环境和增温处理下，深土套中的 SOC 逐渐耗尽，因此整个 SOC 的居留时间随着时间的推移而延长。同时，由于活跃 SOC 超过 50%被耗尽，估计的 SOC 分解的表观和固有温度敏感性也随着时间的推移逐渐升高。因此，深土套中 SOC 分解的温度敏感性与平均 C 居留时间呈正相关。然而，在增温处理下，温度敏感性对居留时间的回归斜率低于环境温度，表明其他过程也调节了 SOC 分解的温度敏感性。这些结果表明，旧 SOC 的分解比年轻组分对温度更敏感，使旧 C 更容易受到未来更暖气候的影响。
