Stomatal uptake and cuticular adsorption contribute to dry deposition of NH3 and NO2 to needles of adult spruce (Picea abies) trees
2002
Geßler, Arthur | Rienks, Michael | Rennenberg, H. (Heinz)
• In the present study NH ₃ and NO ₂ exchange between the atmosphere and needles of adult spruce (Picea abies) trees at a field site (‘Höglwald’) exposed to high loads of atmospheric nitrogen was assessed. • Twigs were fumigated with different NH ₃ (C NH₃) or NO ₂ (C NO₂) concentrations using the dynamic chamber technique. Beside fluxes of NH ₃ (J NH₃) and NO ₂ (J NO₂), transpiration (J H₂O), leaf conductance for water vapour (g H₂O), photosynthetic activity (J cₒ₂), photosynthetic photon fluence rate (PPFR), air temperature (T) and relative air humidity (RH) were determined. • Both fluxes, J NH₃ and J NO₂ , depended linearly on C NH₃ and C NO₂ in concentration ranges representative for the field site and g H₂O as a measure of stomatal aperture. For both trace gases compensation points could be determined amounting to 2.5 nmol mol ⁻¹ for NH ₃ and to 1.7 nmol mol ⁻¹ for NO ₂ . • The fluxes of NH ₃ and NO ₂ could not be explained exclusively by exchange through the stomata. In both NH ₃ and NO ₂ fumigation experiments additional deposition onto the needle surface was observed and increased with increasing C NH₃ and C NO₂ . ¹⁵ N[NH ₃ ] fumigation experiments with adult spruce trees confirmed the results of gas exchange measurements and revealed that NH ₃ ‐N deposited to spruce needles is subjected to long distance transport within the plant, supplying the plant with additional nitrogen from the atmosphere.
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