Association between Carbonyl Sulfide Uptake and ¹⁸Δ during Gas Exchange in C₃ and C₄ Leaves

Abstract

Carbonyl sulfide (COS) and C 18 OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO 2 exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C 3 and C 4 plants, hypothesizing that the rates of COS and C 18OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C 4 and C 3 plants, COS uptake was essentially eliminated and discrimination against C The seasonal cycling of CO 2 concentration measured in the background atmosphere is often taken as evidence of the breathing of Earth and corresponds to about 10 Pg carbon. This is less than 10% of what we estimate to be the total cycling of CO 2 due to respiration and photosynthesis of the terrestrial biosphere (Beer et al., 2010). The discrepancy stems from the fact that most of the cycling CO 2 mixes in the atmosphere near the surface, and we only see the net sum of respiration and photosynthesis, which are often more or less balanced over the seasonal cycle. Modeling and measurements of CO 2 exchange by ecosystems over diurnal cycles have been used to deconvolve the primary biological processes (e.g. Desai et al., 2008). However, our confidence in these approaches disintegrates as we move to larger scales because of the increase in the internal mixing of CO 2 fluxes. Other approaches are needed to quantify the basic physiological processes at these scales.

Stomatal control of leaf fluxes of carbonyl sulfide and CO<sub>2</sub> in a <i>Typha</i> freshwater marsh

“…Leaf level measurements in the laboratory show that LRU is stable at PAR above ca. 500 µmol m −2 s −1 , but increases sharply with decreasing PAR (Stimler et al, 2010(Stimler et al, , 2011. The stable LRU region is consistent with that of light-saturated photosynthesis and maximal stomatal conductance, and therefore low variations in COS and CO 2 fluxes (Stimler et al, 2011).…”

“…LRU is found to decrease with light in both laboratory and field observations (Stimler et al, 2010(Stimler et al, , 2011Maseyk et al, 2014;Commane et al, 2015). Leaf level measurements in the laboratory show that LRU is stable at PAR above ca.…”

“…LRU is the ratio of leaf COS : CO 2 fluxes normalized by their respective ambient concentrations (Sandoval-Soto et al, 2005;Campbell et al, 2008). A mean LRU value of 1.6 has been reported for a wide range of species from leaf scale measurements in the laboratory (Stimler et al, 2010(Stimler et al, , 2011(Stimler et al, , 2012 and the field (Berkelhammer et al, 2014). But in the field, lower LRU values have also been observed, e.g., 1.3 in a wheat field ) and 1.2 in a temperate forest (Commane et al, 2015), both estimated from ecosystem scale measurements.…”

“…Since vegetation uptake dominates the COS exchange in land ecosystems (Berry et al, 2013), concurrent measurements of COS and CO 2 fluxes can be used to separate photosynthesis and respiration from the net carbon flux (Asaf et al, 2013;Billesbach et al, 2014). The COS tracer approach to photosynthesis is based on the coupling of leaf COS and CO 2 uptake (Sandoval-Soto et al, 2005;Seibt et al, 2010;Stimler et al, 2010Stimler et al, , 2011Wohlfahrt et al, 2012).…”

Soil fluxes of carbonyl sulfide (COS), carbon monoxide, and carbon dioxide in a boreal forest in southern Finland

“…Sun et al: Soil COS, CO, and CO 2 fluxes at Hyytiälä COS participates in land carbon cycle processes due to its chemical similarities to CO 2 (Kettle et al, 2002;Montzka et al, 2007;Berry et al, 2013). In leaf chloroplasts and soil microbes, COS as a substrate of carbonic anhydrase is hydrolyzed irreversibly to CO 2 and H 2 S (Protoschill-Krebs and Kesselmeier, 1992;Protoschill-Krebs et al, 1996;Stimler et al, 2010Stimler et al, , 2011Kesselmeier et al, 1999;Saito et al, 2002;Kato et al, 2008;Ogawa et al, 2013). The hydrolysis occurs in parallel to CO 2 hydration, the main physiological function of carbonic anhydrase (Badger and Price, 1994;Henry, 1996).…”