Uptake of NO,NO2 and O3 by sunflower (Helianthus annuus L.) and tobacco plants (Nicotiana tabacum L.): dependence on stomatal conductivity

The uptake of NO, NO₂ and O₃ by sunflowers (Helianthus annuus L. var. giganteus) and tobacco plants (Nicotiana tabacum L. var. Bel W3), using concentrations representative for moderately polluted air, has been determined by gas exchange experiments. Conductivities for these trace gases were measured at different light fluxes ranging from 820 μEm⁻²s⁻¹ to darkness. The conductivities to water vapor and the trace gases are highly correlated. It is concluded that the uptake of NO, NO₂ and O₃ by sunflowers and tobacco plants is linearly dependent on stomatal opening. While the uptake of NO is limited by the mesophyll resistance, the uptake of NO₂ is only by diffusion through the stomata. Loss processes by deposition to the leaf surfaces are more pronounced for O₃ than for NO and NO₂.