Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models
Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models
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DOI：
10.5194/bg-14-5143-2017
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发表时间：
2017-11-17
期刊：
影响因子：
4.9
通讯作者：
Burke, Eleanor J.
中科院分区：
文献类型：
--
作者：
Chadburn, Sarah E.;Krinner, Gerhard;Burke, Eleanor J.
重要的是，气候模型能够准确地模拟北极陆地碳循环，因为在受永冻影响的环境中发现了大量和可能不稳定的碳储存，这可能导致积极的气候反馈，沿着气候变暖下植被向北扩展可能产生碳汇。在这里，我们评估的模拟苔原碳储量和通量在三个陆面方案，每个主要的地球系统模型（JSBACH，德国;朱尔斯，英国; ORCHIDEE，法国）的一部分。我们使用站点级方法，其中全面的高频数据集使我们能够理清不同过程的重要性。该模型改善了物理冻土过程，有一个合理的对应关系的模拟和测量的物理变量，包括土壤温度，土壤湿度和snow.We表明，如果模型模拟正确的叶面积指数（LAI），标准的C3光合作用计划产生正确的数量级的碳通量。因此，模拟正确的LAI是首要任务之一。叶面积指数很大程度上只依赖于气候变量，正如我们所看到的，动态植被模型可以模拟大部分站点之间的叶面积指数差异，几乎完全基于气候输入。然而，我们也确定了营养限制的影响，因为叶面积指数变得太大，在一些更营养有限的网站。我们的结论是，包括苔藓以及维管植物的碳预算是至关重要的，因为苔藓贡献了很大一部分的季节性CO2通量在营养有限的条件下。苔藓的光合作用活性可以强烈地影响苔藓的水分含量，碳吸收可以显着不同的维管植物具有类似的LAI.The土壤碳储量强烈地依赖于从植被到土壤的碳输入速率，我们的分析表明，改善模拟光合作用也会导致改善模拟土壤碳储量。然而，种群也受到土壤碳埋藏（例如通过低温扰动）和异养呼吸速率的影响，这取决于土壤的物理状态。需要进行更详细的地下测量，以充分评估生物和物理土壤过程。此外，即使这些过程被很好地模拟，土壤碳剖面不能像泥炭层一样，因为泥炭积累过程在模型中没有体现出来，因此，我们确定了三个优先领域的模型发展：（1）动态植被，包括（a）气候和（B）养分限制效应;（3）改善了土壤碳的垂直分布，包括泥炭过程。
It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow.We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI.The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models.Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.