Because nitrogen is the mineral nutrient needed in largest amounts by plants, it is usually also the limiting factor for plant growth in terrestrial ecosystems (Vitousek & Howarth, 1991). Consequently, the deposition of oxidized and reduced N compounds will almost invariably have large effects in these systems, and because N availability not only regulates plant growth but also that of organisms at other trophic levels, disturbances of several ecosystem processes might occur. The alternations introduced by deposition of atmospheric N compounds are both of a quantitative and of a qualitative nature. Moreover, N deposition can have phytotoxic as well as growth-stimulating effects.

This short commentary gives a personal view of some of the possible consequences of N deposition on plants. It refers particularly to the oral presentations given by Professor Heinz Rennenberg and Dr Marta Peréz-Soba, and to the discussions held after their talks where appropriate. Separate attention is given to four different consequence of anthropogenic N-deposition: N-availability; N-form, N-uptake by the shoot, and the period of N-uptake. Finally, I have tried to adopt an ecosystem perspective and discuss briefly the concept of critical loads of N.