Seasonal Evolution of Canopy Stomatal Conductance for a Prairie and Maize Field in the Midwestern United States from Continuous Carbonyl Sulfide Fluxes

Abstract

There are inherent challenges in scaling stomatal conductance (g s) from leaf to canopy particularly over seasonal time scales when species distribution and canopy structure evolve. We address this gap using carbonyl sulfide (OCS) and CO 2 fluxes from a predominantly C3 prairie and C4 maize field in the midwestern United States. The g s derived from OCS fluxes captured a transition in the stomatal limitation on gross primary productivity (GPP) through the growing season as well as seasonally persistent g s dynamics such as temperature optimum and a positive response of nighttime g s to vapor pressure deficit. Near the termination of the prairie growing season, we observed a decrease in the relative OCS to CO 2 flux that we hypothesize emerged from a rising contribution of C4 plants to productivity. The results show how plot‐scale OCS and CO 2 fluxes can be used as a trace gas diagnostic for transitions in the limiting factors for community GPP.

Inverse modelling of carbonyl sulfide: implementation, evaluation and implications for the global budget

“…Assimilation of HIPPO observations slightly improves this model bias, which implies that additional observations are urgently required to constrain sources and sinks of COS. We finally find that the biosphere flux dependency on the surface COS mole fraction (which was not accounted for in this study) may substantially lower the fluxes of the SiB4 biosphere model over strong-uptake regions. Using COS mole fractions from our inversion, the prior biosphere flux reduces from 1053 to 851 Gg a −1 , which is closer to 738 Gg a −1 as was found by Berry et al (2013). In planned further studies we will implement this biosphere dependency and additionally assimilate satellite data with the aim of better separating the role of the oceans and the biosphere in the global COS budget.…”

“…Zumkehr et al (2018) recently presented a new global anthropogenic emission inventory for COS. The new anthropogenic emission estimates are, with 406 Gg a −1 (as S equivalents) 1 in 2012, substantially larger than the previous estimate of 180.5 Gg a −1 by Berry et al (2013). Another recent study (Stinecipher et al, 2019) concluded that it is unlikely that biomass burning accounts for the balance between sources and sinks of COS, due to the relatively small contribution of biomass burning to the total emissions ((60 ± 37) Gg a −1 ).…”

“…Carbonyl sulfide (COS or OCS) is a low abundant trace gas in the atmosphere with a lifetime of about 2 years and a tropospheric mole fraction of about 484 pmol mol −1 (Montzka et al, 2007). COS is regarded as a promising diagnostic tool for constraining photosynthetic gross primary production (GPP) of CO 2 through similarities in their stomatal control (Montzka et al, 2007;Campbell et al, 2017;Berry et al, 2013;Whelan et al, 2018;Kooijmans et al, 2017Kooijmans et al, , 2019Wang et al, 2016). COS also contributes to stratospheric sulfur aerosols, which have a cooling effect on climate and hence mitigate climate warming (Crutzen, 1976;Andreae and Crutzen, 1997;Brühl et al, 2012;Kremser et al, 2016).…”

“…Previous studies show that substantial emissions of COS are coming from oceanic, anthropogenic, and biomass burning sources and the largest sinks are uptake by plants and soils (Watts, 2000;Kettle et al, 2002;Berry et al, 2013). Oceanic emissions are thought to be the largest source of COS, both directly and indirectly, due to emissions of CS 2 and possibly DMS (Lennartz et al, 2017(Lennartz et al, , 2020, which can be quickly oxidized to COS in the atmosphere (Sze and Ko, 1980).…”

“…Campbell et al (2008) found that this upward revision could be validated using direct observations from the continental boundary layer from the intensive INTEX-NA airborne campaign. Berry et al (2013) implemented COS in the global biosphere model SiB3. They inferred that, in order to compensate for updated COS biosphere and soil sinks of 1093 Gg a −1 , there must be additional COS sources of 600 Gg a −1 , which were allocated to the ocean.…”