Abstract
Abstract. Global change forces ecosystems to adapt to elevated atmospheric concentrations of carbon dioxide (CO2). We understand that carbonyl sulfide (COS), a trace gas which is involved in building up the stratospheric sulfate aerosol layer, is taken up by vegetation with the same triad of the enzymes which are metabolizing CO2, i.e. ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEP-Co) and carbonic anhydrase (CA). Therefore, we discuss a physiological/biochemical acclimation of these enzymes affecting the sink strength of vegetation for COS. We investigated the acclimation of two European tree species, Fagus sylvatica and Quercus ilex, grown inside chambers under elevated CO2, and determined the exchange characteristics and the content of CA after a 1–2 yr period of acclimation from 350 ppm to 800 ppm CO2. We demonstrate that a compensation point, by definition, does not exist. Instead, we propose to discuss a point of uptake affinity (PUA). The results indicate that such a PUA, the CA activity and the deposition velocities may change and may cause a decrease of the COS uptake by plant ecosystems, at least as long as the enzyme acclimation to CO2 is not surpassed by an increase of atmospheric COS. As a consequence, the atmospheric COS level may rise causing an increase of the radiative forcing in the troposphere. However, this increase is counterbalanced by the stronger input of this trace gas into the stratosphere causing a stronger energy reflection by the stratospheric sulfur aerosol into space (Brühl et al., 2012). These data are very preliminary but may trigger a discussion on COS uptake acclimation to foster measurements with modern analytical instruments.
Highlights
Aside from sulfur dioxide (SO2), carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with relative constant mixing ratios of 450–500 ppt and a lifetime of more than two years (Khalil et al, 1984; Mihalopoulos et al, 1991; Bandy et al, 1992; Barnes et al, 1994; Kjellstrom, 1998; Montzka et al, 2007; Barkley et al, 2008)
We understand that carbonyl sulfide (COS), a trace gas which is involved in building up the stratospheric sulfate aerosol layer, is taken up by vegetation with the same triad of the enzymes which are metabolizing CO2, i.e. ribulose-1,5bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEP-Co) and carbonic anhydrase (CA)
Growth of two European tree species under elevated CO2 for nearly two years resulted in changes of the exchange patterns for CO2 and COS, which in case of Quercus ilex supports the hypothesis that elevated CO2 may lead to a reduction of the COS uptake capacity
Summary
Aside from sulfur dioxide (SO2), carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with relative constant mixing ratios of 450–500 ppt and a lifetime of more than two years (Khalil et al, 1984; Mihalopoulos et al, 1991; Bandy et al, 1992; Barnes et al, 1994; Kjellstrom, 1998; Montzka et al, 2007; Barkley et al, 2008). The global budget of COS has been estimated as being balanced within the ranges of uncertainties (Watts, 2000; Kettle et al, 2002) This balance is a matter of debate both for the sources and the sinks, especially with regard to terrestrial vegetation which acts as the main sink for this trace gas and which is reported to be heavily underestimated (Notholt et al, 2003; Mu et al, 2004; Sandoval-Soto et al, 2005; Campbell et al, 2008; Suntharalingam et al, 2008; Van Diest and Kesselmeier, 2008). This is valid for the Northern Hemisphere, whereas the Southern Hemisphere seems to be strongly influenced by the oceans (Montzka et al, 2007)
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