uptake of gaseous ammonia by the leaves of Italian ryegrass

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.