Effects of atmospheric nitrogen dioxide on uptake and assimilation of ammonium in soybean plants

Abstract

Twelve‐day‐old soybean plants were supplied with 1 mM ammonium chloride (NH₄C1) to roots and exposed to 0.2–0.25 μL.L^‐1 nitrogen dioxide (NO₂) for seven days. Amount and rate of ammonium uptake were decreased by NO₂ exposure. However, the ammonium concentration in leaves and leaf pH of exposed plants were increased by NO₂ exposure. These results suggest that the decrease in ammonium uptake may be due to the decline in hydrogen (H⁺) ion concentration in exposed plants which resulted from the reduction of the nitrate and nitrite from NO₂ absorption. They also suggest that the decrease in ammonium uptake and the competition for energy between nitrate reduction and ammonium assimilation may limit ammonium assimilation to organic nitrogen (N) which would further inhibit acidity increase in exposed plants and ammonium uptake by roots.