The Influence of Plant Nitrogen Status on NO2Uptake, NO2Assimilation and on the Gas Exchange Characteristics of Barley Plants Exposed to Atmospheric NO2

Abstract

Barley plants were grown in nutrient solution at two contrasting nitrate concentrations to produce plants of low or high nitrogen (N) status. Leaves were then exposed continuously to either 0.3 mm³ dm⁻³ NO₂ or clean air, with the roots and rooting medium isolated from the polluted air. Uptake of NO₂ was measured in two ways; as depletion from an air stream containing the gas and using ¹⁵N-labelled NO₂. Results from the two methods agreed well and demonstrated that the flux of NO₂ into the leaves of N-deficient barley was lower than that of N-sufficient plants. Nevertheless, the relative contribution of¹⁵N derived from ¹⁵NO₂ to the N status of the plant was greater in the plants supplied with low nitrate. A major factor in regulating NO₂ uptake by barley leaves appeared to be stomatal conductance, although internal conductance may also be involved. The effects of NO₂ exposure of barley on carbon dioxide exchange rates, transpiration and water vapour conductance were also influenced by the N status of the plant.