Optimizing the carbonic anhydrase temperature response and stomatal conductance of carbonyl sulfide leaf uptake in the Simple Biosphere model (SiB4)
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Published:2023-07-05
Issue:13
Volume:20
Page:2573-2594
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Cho Ara, Kooijmans Linda M. J.ORCID, Kohonen Kukka-MaariaORCID, Wehr RichardORCID, Krol Maarten C.ORCID
Abstract
Abstract. Carbonyl sulfide (COS) is a useful tracer to estimate
gross primary production (GPP) because it shares part of the uptake pathway
with CO2. COS is taken up in plants through hydrolysis, catalyzed by
the enzyme carbonic anhydrase (CA), but is not released. The Simple
Biosphere model version 4 (SiB4) simulates COS leaf uptake using a
conductance approach. SiB4 applies the temperature response of the RuBisCo
enzyme (used for photosynthesis) to simulate the COS leaf uptake, but the CA enzyme might respond differently to temperature. We introduce a new
temperature response function for CA in SiB4, based on enzyme kinetics with
an optimum temperature. Moreover, we determine Ball–Woodrow–Berry (BWB)
model parameters for stomatal conductance (gs) using observation-based estimates of COS flux, GPP, and gs along with meteorological measurements in an evergreen needleleaf forest (ENF) and deciduous broadleaf forest (DBF). We find that CA has optimum temperatures of 20 ∘C (ENF) and 36 ∘C (DBF), which is lower than that of RuBisCo (45 ∘C), suggesting that canopy temperature changes can critically affect CA's catalyzation activity. Optimized values for the BWB offset parameter are similar to the original value (0.010 ± 0.003 mol m−2 s−1), and optimized values for the BWB slope parameter (ENF: 16.4, DBF: 11.4) are higher than the original value (9.0) at both sites. The optimization reduces prior errors on all parameters by more than 50 % at both stations. We apply the optimized gi and gs parameters in
SiB4 site simulations, thereby improving the timing and peak of COS
assimilation. In addition, we show that SiB4 underestimates the leaf
humidity stress under conditions where high vapor pressure deficit (VPD) should limit gs in the afternoon, thereby overestimating gs. Furthermore, global COS biosphere sinks with optimized parameters show smaller COS uptake in regions where the air temperature is over 25 ∘C, mostly in the tropics, and larger uptake in regions where the temperature is below 25 ∘C. This change
corresponds with reported deficiencies in the global COS fluxes, such as
missing sinks at high latitudes and required sources in the tropics. Using
our optimization and additional observations of COS uptake over various
climate and plant types, we expect further improvements in global COS
biosphere flux estimates.
Funder
H2020 European Research Council
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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