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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Maignan , F , Abadie , C , Remaud , M , Kooijmans , L M J , Kohonen , K-M , Commane , R , Wehr , R , Campbell , J E , Belviso , S , Montzka , S A , Raoult , N , Seibt , U , Shiga , Y P , Vuichard , N , Whelan , M E & Peylin , P 2021 , ' Carbonyl sulfide : comparing a mechanistic representation of the vegetation uptake in a land surface model and the leaf relative uptake approach ' , Biogeosciences , vol. 18 , no. 9 , pp. 2917–2955 . https://doi.org/10.5194/bg-18-2917-2021

Title: Carbonyl sulfide : comparing a mechanistic representation of the vegetation uptake in a land surface model and the leaf relative uptake approach
Author: Maignan, Fabienne; Abadie, Camille; Remaud, Marine; Kooijmans, Linda M. J.; Kohonen, Kukka-Maaria; Commane, Róisín; Wehr, Richard; Campbell, J. Elliott; Belviso, Sauveur; Montzka, Stephen A.; Raoult, Nina; Seibt, Ulli; Shiga, Yoichi P.; Vuichard, Nicolas; Whelan, Mary E.; Peylin, Philippe
Contributor: University of Helsinki, Department of Physics
Date: 2021-05-12
Language: eng
Number of pages: 39
Belongs to series: Biogeosciences
ISSN: 1726-4170
URI: http://hdl.handle.net/10138/330310
Abstract: 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.
Subject: 1181 Ecology, evolutionary biology
1172 Environmental sciences
1171 Geosciences
EULERIAN BACKTRACKING
MESOPHYLL CONDUCTANCE
STOMATAL CONDUCTANCE
ATMOSPHERIC TRACERS
GENERAL-CIRCULATION
BIOCHEMICAL-MODEL
WATER TRANSPORT
GAS-EXCHANGE
CO2
DIOXIDE
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