THE EFFECTS OF ROOT NITROGEN SUPPLIES ON THE ABSORPTION OF ATMOSPHERIC NO2 BY SOYBEAN LEAVES

Twelve-day-old soybean plants were exposed to atmospheric NO2 (0.3 mu l l(-1)) and simultaneously supplied, via the roots, with 5 mM or 1 mM of NaNO3 or NH4Cl. After exposure for 7 d, the amount of NO2, absorbe d per plant was greater in plants supplied with nitrate than in plants supplied with the same concentration of ammonium. The NO, AR (absorpt ion rate) decreased with increasing exposure time. At the beginning of exposure, the NO, AR for all plants was c. 12 mg NO(2)h(-1) m(-2) mu l(-1) l. On the day 7 of exposure, the NO, AR declined to 8.46, 8.97, 8.27, and 9.04 mg NO(2)h(-1) m(-2) mu l(-1) l for plants receiving 1 m M ammonium, 1 mM nitrate, 5 mM ammonium, and 5 mM nitrate respectively . The plants supplied with nitrate had a higher concentration of leaf nitrate and a higher pH than those supplied with the equivalent concen tration of ammonium. These results suggest that the NO2 absorption rat e might be attenuated by the accumulation of H+ produced from N uptake and assimilation.