Nitrogen saturation experiments (NITREX) in coniferous forest ecosystems in Europe: a summary of results

Tietema A. 1, Boxman A.W. 2, Bredemeier M. 3, Emmett B.A. 4, Moldan F. 5, Gundersen P. 6, Schleppi P. 7, Wright R.F. 8

1 Univ. Amsterdam, The Netherlands Center for Geo-ecological Research, NL-1018 VZ Amsterdam
2 Univ. Nijmegen, Dept. Ecol., NL-6500 GL Nijmegen
3 Univ. Göttingen, Forest Ecosyst. Res. Ctr., D-37077 Göttingen
4 Inst. Terr. Ecol., Bangor Res. Unit, Bangor LL57 2UP, UK
5 Swedish Environm. Res. Inst., S-40285 Göteborg
6 Danish Forest and Landscape Res. Inst., DK-2970 Hørsholm
7 Swiss Fed. Inst. Forest Snow and Landscape Res., CH-8903 Birmensdorf
8 Norwegian Inst. Water Res., N-0411 Oslo

Environ. Pollut. 102 (S1) (1998): 433-437

DOI: 10.1016/S0269-7491(98)80065-1


The effect of changes in dissolved inorganic nitrogen (N) deposition on ecosystem functioning was investigated in the NITREX (NITRogen saturation EXperiments) project. Field-scale manipulation experiments were carried out over four to six years in seven coniferous forest ecosystems in northwestern Europe. At sites with low or moderate ambient N deposition, N was experimentally added to throughfall. At sites with high N deposition, N was removed from throughfall. We found that the capacity of the ecosystem to retain N was correlated to its internal N status. Some of the components of this N status like the N concentrations in foliage and forest floor are relatively easy to measure. The C/N ratio of the forest floor is especially closely related to the onset of nitrate leaching. Changes in N input may, in the long run, change the N status of an ecosystem due to for instance a decrease in C/N ratio in the forest floor. Decreased N input resulted in a rapid and large reduction in N concentration in drainage water. Significant improvement in tree nutritional status, tree growth, fine root biomass and diversity of ground vegetation and mycorrhizal fungi population were observed in one site only. The time period of four to six years of manipulated N deposition may have been too short for changes to be manifested in the other sites.

Keywords: NITREX, nitrogen deposition, coniferous forests, nitrogen saturation,