Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)
Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)
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DOI：
10.5194/bg-18-6547-2021
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发表时间：
2021-12-22
期刊：
影响因子：
4.9
通讯作者：
Krol, Maarten
中科院分区：
文献类型：
--
作者：
Kooijmans, Linda M. J.;Cho, Ara;Krol, Maarten
陆地植物对硫化羰 (COS) 的吸收与光合作用对二氧化碳的吸收有关，因为这些气体部分共享相同的吸收途径。在模型中应用 COS 作为光合作用示踪剂需要准确表示生物圈 COS 通量，但这些模型尚未针对 COS 通量的现场观测进行广泛评估。在本文中，简单生物圈模型第 4 版 (SiB4) 模拟的 COS 通量更新了最新的机制见解，并通过不同生物群落的现场观察进行了评估：一片常绿针叶林、两片落叶阔叶林、三片草地和两片分布在欧洲和北美的农田。我们通过多种方式改进了 SiB4，以改善其对 COS 的表征。为了考虑大气 COS 摩尔分数对 COS 生物圈吸收的影响，我们用空间和时间变化的 COS 摩尔分数场替换了最初在 SiB4 中使用的固定大气 COS 摩尔分数边界条件。在调查地点，COS 摩尔分数的季节性幅度类似于 50-200 ppt，在生长季节后期摩尔分数最小。将季节变化纳入模型中可以降低生长季节后期的 COS 吸收率，从而与观测结果更好地吻合。我们还将 SiB4 中的经验土壤 COS 吸收模型替换为代表土壤中 COS 吸收和生产的机械模型，这提高了与农田和施肥草地土壤观测的匹配度。 SiB4 的改进版本能够模拟北方、温带和地中海地区 COS 通量的昼夜和季节变化。尽管如此，白天植被 COS 通量平均被低估了 8 +/- 27%，尽管不同地点之间差异很大。在全球范围内，我们的模型修改将模拟的 COS 陆地生物圈汇从原始 SiB4 中的 922 Gg S yr(-1) 减少到更新版本中的 753 Gg S yr(-1)。通量下降幅度最大的原因是生产力高的地区大气 COS 摩尔分数较低，这凸显了考虑大气 COS 摩尔分数变化的重要性。另一方面，改变不同的土壤模型对全球生物圈 COS 汇的影响相对较小。模拟土壤成分在全球 COS 预算中的次要作用支持使用 COS 作为全球光合作用示踪剂。更准确地表示 SiB4 中 COS 的吸收应该可以改进大气 COS 作为局部到全球范围陆地光合作用示踪剂的应用。
The uptake of carbonyl sulfide (COS) by terrestrial plants is linked to photosynthetic uptake of CO2 as these gases partly share the same uptake pathway. Applying COS as a photosynthesis tracer in models requires an accurate representation of biosphere COS fluxes, but these models have not been extensively evaluated against field observations of COS fluxes. In this paper, the COS flux as simulated by the Simple Biosphere Model, version 4 (SiB4), is updated with the latest mechanistic insights and evaluated with site obser- vations from different biomes: one evergreen needleleaf forest, two deciduous broadleaf forests, three grasslands, and two crop fields spread over Europe and North America. We improved SiB4 in several ways to improve its representation of COS. To account for the effect of atmospheric COS mole fractions on COS biosphere uptake, we replaced the fixed atmospheric COS mole fraction boundary condition originally used in SiB4 with spatially and temporally varying COS mole fraction fields. Seasonal amplitudes of COS mole fractions are similar to 50-200 ppt at the investigated sites with a minimum mole fraction in the late growing season. Incorporating seasonal variability into the model reduces COS uptake rates in the late growing season, allowing better agreement with observations. We also replaced the empirical soil COS uptake model in SiB4 with a mechanistic model that represents both uptake and production of COS in soils, which improves the match with observations over agricultural fields and fertilized grassland soils. The improved version of SiB4 was capable of simulating the diurnal and seasonal variation in COS fluxes in the boreal, temperate, and Mediterranean region. Nonetheless, the daytime vegetation COS flux is underestimated on average by 8 +/- 27 %, albeit with large variability across sites. On a global scale, our model modifications decreased the modeled COS terrestrial biosphere sink from 922 Gg S yr(-1) in the original SiB4 to 753 Gg S yr(-1) in the updated version. The largest decrease in fluxes was driven by lower atmospheric COS mole fractions over regions with high productivity, which highlights the importance of accounting for variations in atmospheric COS mole fractions. The change to a different soil model, on the other hand, had a relatively small effect on the global biosphere COS sink. The secondary role of the modeled soil component in the global COS budget supports the use of COS as a global photosynthesis tracer. A more accurate representation of COS uptake in SiB4 should allow for improved application of atmospheric COS as a tracer of local- to global-scale terrestrial photosynthesis.