Can we model observed soil carbon changes from a dense inventory? A case study over England and Wales using three versions of the ORCHIDEE ecosystem model (AR5, AR5-PRIM and O-CN)
Can we model observed soil carbon changes from a dense inventory? A case study over England and Wales using three versions of the ORCHIDEE ecosystem model (AR5, AR5-PRIM and O-CN)
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DOI：
10.5194/gmd-6-2153-2013
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发表时间：
2013-12
影响因子：
5.1
通讯作者：
B. Guenet;F. Moyano;N. Vuichard;G. Kirk;P. Bellamy;S. Zaehle;P. Ciais
中科院分区：
文献类型：
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作者：
B. Guenet;F. Moyano;N. Vuichard;G. Kirk;P. Bellamy;S. Zaehle;P. Ciais
抽象的。 1978-2003 年期间，国家土壤清单 (NSI) 观察到英格兰和威尔士表土碳含量普遍下降，相当于 141 550 km2 面积上的碳损失达 4.44 Tg yr−1。随后的模型研究表明，温度和降水的变化只能解释观测到的减少的一小部分，因此土地利用和管理的变化以及由此导致的异养呼吸或净初级生产力的变化是主要原因。到目前为止，所有用于重现 NSI 数据的模型都没有考虑植物与土壤的相互作用，而只是由数据强制碳输入的土壤碳模型。在这里，我们使用了名为 ORCHIDEE（动态生态系统中的碳和水文组织）的基于过程的土壤-植被耦合模型的三个不同版本，以便将土壤碳输入趋势的影响与 1978-2003 年气候趋势引起的土壤碳矿化的影响分开。该模型的第一个版本 (ORCHIDEE-AR5) 用于 IPCC-AR5 CMIP5 地球系统模拟，基于用一级分解动力学定义的三个土壤碳库，如 CENTURY 模型中那样。为本研究构建的第二个版本 (ORCHIDEE-AR5-PRIM) 包括凋落物碳和分解速率之间的关系，以重现分解的启动效应。最后一个版本（O-CN）考虑了N个相关进程。 O-CN 中的土壤碳分解基于 CENTURY，但增加了对凋落物分解的 N 限制。我们使用这三个版本的 ORCHIDEE 模型在英格兰和威尔士进行了区域网格模拟。三个模型版本均无法重现观察到的 NSI 土壤碳趋势。这表明要么气候变化不是观测到的土壤碳损失的主要驱动因素，要么ORCHIDEE模型即使具有启动或氮对分解的影响也缺乏解释气候响应土壤碳变化的基本机制，这将对此类模型预测土壤碳变化响应未来变暖的能力提出警告。第三种可能的解释是，对表土进行的 NSI 测量并不代表整个土壤深度的土壤碳损失总量，因此无法与模型输出进行比较。
Abstract. A widespread decrease of the topsoil carbon content was observed over England and Wales during the period 1978–2003 in the National Soil Inventory (NSI), amounting to a carbon loss of 4.44 Tg yr−1 over 141 550 km2. Subsequent modelling studies have shown that changes in temperature and precipitation could only account for a small part of the observed decrease, and therefore that changes in land use and management and resulting changes in heterotrophic respiration or net primary productivity were the main causes. So far, all the models used to reproduce the NSI data have not accounted for plant–soil interactions and have only been soil carbon models with carbon inputs forced by data. Here, we use three different versions of a process-based coupled soil–vegetation model called ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems), in order to separate the effect of trends in soil carbon input from soil carbon mineralization induced by climate trends over 1978–2003. The first version of the model (ORCHIDEE-AR5), used for IPCC-AR5 CMIP5 Earth System simulations, is based on three soil carbon pools defined with first-order decomposition kinetics, as in the CENTURY model. The second version (ORCHIDEE-AR5-PRIM) built for this study includes a relationship between litter carbon and decomposition rates, to reproduce a priming effect on decomposition. The last version (O-CN) takes into account N-related processes. Soil carbon decomposition in O-CN is based on CENTURY, but adds N limitations on litter decomposition. We performed regional gridded simulations with these three versions of the ORCHIDEE model over England and Wales. None of the three model versions was able to reproduce the observed NSI soil carbon trend. This suggests either that climate change is not the main driver for observed soil carbon losses or that the ORCHIDEE model even with priming or N effects on decomposition lacks the basic mechanisms to explain soil carbon change in response to climate, which would raise a caution flag about the ability of this type of model to project soil carbon changes in response to future warming. A third possible explanation could be that the NSI measurements made on the topsoil are not representative of the total soil carbon losses integrated over the entire soil depth, and thus cannot be compared with the model output.