Figure 1.

Comparison of the diffusion pathways of COS and CO₂ from the atmosphere to the site of biochemical reactions in C₃ and C₄ leaves. Concentrations of COS (pmol mol⁻¹) and CO₂ (μmol mol⁻¹) are indicated above and below the lines, respectively. Conductance through resistance steps associated with the boundary layer, stomata, and mesophyll (mol m⁻² s⁻¹) are indicated by g_bl, g_s, and g_m, respectively, based on leaves with net CO₂ flux of 14 or 20 μmol m⁻² s⁻¹ (C₃ and C₄, respectively), and COS uptake flux of approximately 35 pmol m⁻² s⁻¹ (for both plant types). Values of g_m (0.3 mol m⁻² s⁻¹ for both C₄ and C₃ leaves, respectively) were estimated by Stimler et al. (2010a) and incorporate dissolution, liquid-phase diffusion, and the biochemical step (assuming first-order reaction); g_m estimates for CO₂ were based on CO₂ concentration at the hydration site derived from isotopic measurements (Gillon and Yakir, 2001).