The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass

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Abstract
Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseous ammonia by the leaves of Italian ryegrass.—J. exp. Bot. 37: 919–927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown in soil with two rates of added 15N-labelled nitrate were exposed, in chambers, for 40 d to NH3 in the air at concentrations of 16, 118 and 520 μg m−3. At the highest concentration of NH3, this source provided 47·3% of the total nitrogen in plants grown with the lower rate of nitrate addition (100mg N kg−1 dry soil) and 35·2% with the higher rate (200mg N kg−1 dry soil) At the intermediate concentration of NH3, the contributions to total plant N were 19·6% and 10·8%, respectively, at low and high nitrate while, at the lowest concentration of NH3, they were 5·1% and 32%. Most of the N derived from the NH3 remained in the leaves, but some was transported to the roots. The amount of N derived from the NH3 that was present in the leaves was not reduced by washing the leaves in water at pH 5·0 before harvesting, indicating that the N was assimilated by the plant and not adsorbed superficially. Rates of uptake of NH3 per unit leaf area ranged from 1·7 μg dm−2 h−1 at a concentration of 16 μg m−3 to 29·0 μg dm−2 h−1 at a concentration of 520 μg m−3 and with the lower rate of nitrate addition. Increasing the supply of nitrate to the roots slightly reduced the rate of uptake of NH3 per unit leaf area. Uptake of N from the higher rate of nitrate was reduced at the highest concentration of NH3 in the air.