The Influence of the Concentration of Gaseous Ammonia on its Uptake by the Leaves of Italian Ryegrass, with and without an Adequate Supply of Nitrogen to the Roots

Whitehead, D. C. and Lockyer, D. R. 1986. The influence of the concentration of gaseous ammonia on its uptake by the leaves of Italian ryegrass, with and without an adequate supply of nitrogen to the roots.—J. exp. Bot. 38: 818–827. Plants of Italian ryegrass (Lolium multiflorum Lam.) were grown in pots of soil with two rates of 15N-labclled nitrate, one providing adequate, and the other less than adequate, N for maximum growth. After 25 d in a controlled environment cabinet, the plants were transferred to chambers and exposed for 33 d to NH3in the air at one of nine concentrations ranging from 14 to 709 μg NH3 m−3. Increasing the concentration of NH3 in the air increased the dry weight of the shoots of plants grown at the lower but not the higher rate of nitrate. The content of total N in the plant shoots (% dry weight) was linearly related to NH3 concentration; at 709 μg NH3 and in both sets of plants it was more than double the content at 14 μg NH3 m−3. Calculations, based on 15N enrichment, indicated that the amount of N taken up from the NH3 per unit leaf area increased linearly with increasing concentration of NH3 in the air uptake (μg dm−2 h−1) = 0.1009x at the lower rate of nitrate and 0-0829x at the higher rate of nitrate, where x is the concentration of NH3 in the air expressed as μg NH3m−3. The proportion of the total plant N that was derived from the NH3 ranged from 4·0% at a concentration of 14 μg NH3 m−3 with the higher rate of nitrate addition to 77·5% at a concentration of 709 μg m−3 with the lower rate of nitrate addition. The proportions of the total N in the water-insoluble protein of the leaf tissue that were derived from nitrate and gaseous NH3 were similar to the proportions in the whole leaf material.