Carbonyl sulfide: comparing a mechanistic representation of the vegetation uptake in a land surface model and the leaf relative uptake approach
Carbonyl sulfide: comparing a mechanistic representation of the vegetation uptake in a land surface model and the leaf relative uptake approach
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DOI：
10.5194/bg-18-2917-2021
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发表时间：
2021-05-12
期刊：
影响因子：
4.9
通讯作者：
Peylin, Philippe
中科院分区：
文献类型：
--
作者：
Maignan, Fabienne;Abadie, Camille;Peylin, Philippe
陆地表面模型需要可测量的替代物来限制大陆植物通过光合作用吸收的二氧化碳（CO2）的数量，称为总初级生产力（GPP）。羰基硫（COS），这是采取了叶片通过气孔，然后由光合酶水解，是一个候选的GPP代理。之前使用ORCHIDEE陆面模型的一项研究使用固定的COS吸收与CO2吸收比率（标准化为每种植被类型各自的环境浓度（叶相对吸收，LRU））来计算GPP的植被COS通量。已知LRU方法具有有限的准确性，因为LRU比率随着诸如光合有效辐射（PAR）的变量而变化：虽然CO2吸收在低光下减慢，但COS吸收不受光限制。然而，LRU方法一直流行的COS-GPP代理研究，因为它易于应用和明显的区域尺度应用的不确定性的贡献低。在这项研究中，我们完善了COS-GPP关系，并在ORCHIDEE中实现了一个描述大陆植被吸收COS的机制模型。我们比较了模拟的COS通量与两个站点每小时测量的COS通量，并研究了模型行为和与环境驱动因素的联系。我们在全球范围内进行了模拟，我们估计全球植被对COS的吸收量为-756 Gg S yr（-1），在以前研究的中间范围（-490至-1335 Gg S yr（-1））。基于在ORCHIDEE的机械方法模拟的月平均通量，我们得出了新的LRU值为不同的植被类型，范围在0.92和1.72之间，接近最近公布的平均观测值为1.21 C-4和1.68 C-3植物。我们运送COS使用每月的植被COS通量来自机械和LRU的方法，我们评估了模拟COS浓度在NOAA网站。虽然机制的方法是更合适的高时间分辨率的COS通量测量相比，这两种方法得到了类似的结果时，每月输送COS通量和评估COS浓度站。在我们的研究中，这两种方法之间的不确定性是次要的COS全球预算的不确定性，这是目前的一个限制因素，COS浓度的潜力，以限制在全球范围内的陆面模式模拟的GPP相比。
Land surface modellers need measurable proxies to constrain the quantity of carbon dioxide (CO2) assimilated by continental plants through photosynthesis, known as gross primary production (GPP). Carbonyl sulfide (COS), which is taken up by leaves through their stomates and then hydrolysed by photosynthetic enzymes, is a candidate GPP proxy. A former study with the ORCHIDEE land surface model used a fixed ratio of COS uptake to CO2 uptake normalised to respective ambient concentrations for each vegetation type (leaf relative uptake, LRU) to compute vegetation COS fluxes from GPP. The LRU approach is known to have limited accuracy since the LRU ratio changes with variables such as photosynthetically active radiation (PAR): while CO2 uptake slows under low light, COS uptake is not light limited. However, the LRU approach has been popular for COS-GPP proxy studies because of its ease of application and apparent low contribution to uncertainty for regional-scale applications. In this study we refined the COS-GPP relationship and implemented in ORCHIDEE a mechanistic model that describes COS uptake by continental vegetation. We compared the simulated COS fluxes against measured hourly COS fluxes at two sites and studied the model behaviour and links with environmental drivers. We performed simulations at a global scale, and we estimated the global COS uptake by vegetation to be -756 Gg S yr(-1) , in the middle range of former studies (-490 to -1335 Gg S yr(-1)). Based on monthly mean fluxes simulated by the mechanistic approach in ORCHIDEE, we derived new LRU values for the different vegetation types, ranging between 0.92 and 1.72, close to recently published averages for observed values of 1.21 for C-4 and 1.68 for C-3 plants. We transported the COS using the monthly vegetation COS fluxes derived from both the mechanistic and the LRU approaches, and we evaluated the simulated COS concentrations at NOAA sites. Although the mechanistic approach was more appropriate when comparing to high-temporal-resolution COS flux measurements, both approaches gave similar results when transporting with monthly COS fluxes and evaluating COS concentrations at stations. In our study, uncertainties between these two approaches are of secondary importance compared to the uncertainties in the COS global budget, which are currently a limiting factor to the potential of COS concentrations to constrain GPP simulated by land surface models on the global scale.