Dependency of nitrogen dioxide (NO 2) fluxes to wheat ( Triticum aestivum L.) leaves from NO 2 concentration, light intensity, temperature and relative humidity determined from controlled dynamic chamber experiments

Abstract

The dynamic chamber technique was applied to investigate the dependency of nitrogen dioxide fluxes to wheat leaves from atmospheric NO 2 concentration, light intensity, air temperature and relative humidity. Experiments were performed with 4- to 5-weeks-old wheat plants under controlled environmental conditions. When exposed to NO 2-free air wheat leaves emitted 3.7 ng N m −2 s −1into the atmosphere. With increasing NO 2 concentrations the flux of NO 2 changed from emission to deposition. Up to NO 2 concentrations of 60 nl ℓ −1 the NO 2 flux increased linearly; at higher concentrations of NO 2 the NO 2 flux further increased, but the increment declined. In the range of NO 2 concentrations studied (0–90 nl ℓ −1) neither transpiration nor photosynthesis was affected by the NO 2 exposure. With increasing light intensity NO 2 deposition increased from 29 ng N m −2 s −1 in the dark to 120 ng N m −2 s −1 at 510 μmol m −2 s −1 PAR, when wheat plants were exposed to 30 nl ℓ −1 NO 2. This effect could be attributed to the light dependent increase in stomatal aperture. With increasing air temperature from 17 to 40°C NO 2 deposition decreased, most likely due to decreasing solubility of NO 2 in the aqueous phase of the apoplastic space. NO 2 deposition also increased with increasing relative humidity. This increase could not be explained by changes in stomatal aperture, but may at least partially be due to the formation of ultra thin water films on the surface of the wheat leaves, and the solubilization of atmospheric NO 2 within these water films.