Global uptake of carbonyl sulfide (COS) by terrestrial vegetation: Estimates corrected by deposition velocities normalized to the uptake of carbon dioxide (CO<sub>2</sub>)

Abstract

Abstract. COS uptake by trees, as observed under dark/light changes and under application of the plant hormone abscisic acid, exhibited a strong correlation with the CO2 assimilation rate and the stomatal conductance. As the uptake of COS occurred exclusively through the stomata we compared experimentally derived and re-evaluated deposition velocities (Vd for COS and CO2). We show that Vd of COS is generally significantly larger than that of CO2. We therefore introduced this attribute into a new global estimate of COS fluxes into vegetation. The global COS uptake by vegetation as estimated by the new model ranges between 0.69-1.40 Tg a-1, based on the Net Primary Productivity (NPP). Taking into account Gross Primary Productivity (GPP) the deposition estimate ranges between 1.37-2.81 Tg a-1 (0.73-1.50 Tg S a-1). We believe that in order to obtain accurate and reliable global NPP-based estimates for the COS flux into vegetation, the different deposition velocities of COS and CO2 must be taken into account.

On the global distribution, seasonality, and budget of atmospheric carbonyl sulfide (COS) and some similarities to CO2

“…(c) Same as Figure 9b, but with fluxes to vegetation derived from net primary productivity (NPP) (as given by Kettle et al [2002a]) multiplied by a factor of 5 (see text) (note scale change compared to Figures 9a and 9b). This factor is within the range suggested by Sandoval‐Soto et al [2005], who proposed vegetative losses for COS that are 3 to 6 times greater than derived by Kettle et al [2002a] from scaling NPP by (X COS /X CO2 ).…”

“… c Corresponds to 3 and 6 times net primary productivity × (X COS /X CO2 ) as estimated by Kettle et al [2002a], as by Sandoval‐Soto et al [2005]; see also considerations discussed in the text. …”

“…The uptake by vegetation has been recognized for many years as a dominant sink for atmospheric COS [ Brown and Bell , 1986; Goldan et al , 1988; Kjellström , 1998; Kettle et al , 2002a; Xu et al , 2002; Sandoval‐Soto et al , 2005]. Substantial uptake of COS by vegetation is expected because it undergoes rapid hydrolysis by enzymes present in leaf water that are involved in the initial stages of photosynthesis: carbonic anhydrase, rubisco, and PEP carboxylase [ Protoschill‐Krebs and Kesselmeier , 1992; Protoschill‐Krebs et al , 1996].…”

“…Studies with radioactively labeled sulfur in COS show that sulfur taken up as COS by vegetation becomes incorporated into plant amino acids and proteins [ Brown et al , 1986; Kluczewski et al , 1985]. The uptake of COS and CO 2 by photosynthetically active vegetation is modulated by the activity of these enzymes and by leaf stomatal conductance [ Kesselmeier and Merk , 1993; Gillon and Yakir , 2001; Sandoval‐Soto et al , 2005; Yonemura et al , 2005].…”

High precision measurements of atmospheric concentrations and plant exchange rates of carbonyl sulfide using mid‐IR quantum cascade laser

“…Carbonyl sulfide (COS) was recently proposed as a potential tracer of gross CO 2 uptake by terrestrial vegetation, based, in part, on the assumption that COS uptake by vegetation is associated with photosynthetic CO 2 uptake, but not with respiration (Kesselemier & Merk, 1993;Protoschill-Krebs et al, 1996;Sandoval-Soto et al, 2005;Yonemura et al, 2005), consistent with global observations and modeling of the seasonal variation of atmospheric CO 2 and COS concentrations and modeling (Montzka et al, 2007;Campbell et al, 2008). Because, unlike CO 2 , COS is assumed not to be emitted by vegetation, it is a potentially powerful tracer of gross photosynthesis, and coupling COS and CO 2 measurements may provide much needed process-based insights into ecosystem response to changes in environmental conditions.…”