Plant and Soil, March, 1996, Vol.180(2), p.197
Byline: Paul Weber (2), Heinz Rennenberg (2) Keywords: dynamic chamber; gas exchange; nitrogen dioxide; nitric oxide; wheat canopy monolith Abstract: The fluxes of NO and NO.sub.2 between wheat canopy monoliths and the atmosphere were investigated with the dynamic chamber technique. For this purpose monoliths were dug out at different plant growth stages from a field site, transported to the institute, and placed in an environmental growth chamber. The wheat canopy monoliths were exposed over a period of four days to the average ratios of atmospheric NO.sub.2 and NO measured at the field site, i.e. NO.sub.2 concentration of about 18 mL L.sup.-1 plus NO concentration lower than 0.5 nL L.sup.-1. Under these conditions NO emission into the atmosphere and NO.sub.2 deposition into canopy monoliths was observed. Both fluxes showed diurnal variation with maximum rates during the light and minimum rates during darkness. NO.sub.2 fluxes correlated with soil temperature as well as with light intensity. NO fluxes correlated with soil temperature but not with light intensity. From the investigation performed the diurnal variation of the NO and NO.sub.2 compensation points, the maximum rates of NO and NO.sub.2 emission, and the total resistances of NO and NO.sub.2 fluxes were calculated. Under the assumption that the measured data are representative for the whole vegetation period, annual fluxes of NO and NO.sub.2 were estimated. Annual NO emission into the atmosphere amounted to 87 mg N m.sup.-2 y.sup.-1 (0.87 kg ha.sup.-1 y.sup.-1), annual NO.sub.2 deposition into canopy monoliths amounted to 1273 mg N m.sup.-2 y.sup.-1 (12.73 kg ha.sup.-1 y.sup.-1). Apparently, the uptake of atmospheric nitrogen by the wheat field from NO.sub.2 deposition is about 15 times higher than the loss of nitrogen from NO emission. It can therefore be assumed that even in rural areas wheat fields are a considerable sink for atmospheric nitrogen. The annual sink strength estimated in the present study is ca. 12 kg N ha.sup.-1 y.sup.-1. The possible origin of the NO emitted and the fate of atmospheric NO.sub.2 taken up by the wheat canopy monoliths are discussed. Author Affiliation: (2) Fraunhofer-Institut fur Atmospharische Umweltforschung, Kreuzeckbahn str. 19, D-82467, Garmisch-Partenkirchen, Germany (3) Institut fur Forstbotanik und Baumphysiologie, Professur fur Baumphysiologie, Albert-Ludwigs-Universitat Freiburg, Am Flughafen 1.7, D-79085, Freiburg i. Br., Germany Article History: Registration Date: 07/04/2004 Received Date: 11/08/1995 Accepted Date: 18/12/1995 Article note: Preliminary results of this paper were presented at the Joint Workshop COST 611/Working Party 3 and EUROTRAC in Delft, The Netherlands (Ludwig et al., 1991).
Wheat ; Nitric Oxide
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