Qualitative and quantitative changes in plant nitrogen acquisition induced by anthropogenic nitrogen deposition

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.