Abstract
Patterns of nitrogen (N) isotope composition (δ15 N) and total N contents were determined in leaves, fine roots, root-associated ectomycorrhizal fungi (ECM) of adult beech trees (Fagus sylvatica), and soil material under ambient (1 × O3 ) and double ambient (2 × O3 ) atmospheric ozone concentrations over a period of two years. From fine root to leaf material δ15 N decreased consecutively. Under enhanced ozone concentrations total N was reduced in fine roots and δ15 N showed a decrease in roots and leaves. In the soil and in most types of mycorrhizae, δ15 N and total N were not altered due to ozone fumigation. The number of vital ectomycorrhizal root tips increased and the mycorrhizal community structure changed in 2 × O3 . Simultaneously, the specific rate of inorganic N-uptake by the roots was reduced under the double ozone regime. From these results it is assumed that 2 × O3 changes N-nutrition of the trees at the level of N-acquisition, as indicated by enhanced mycorrhizal root tip density, altered mycorrhizal species composition, and reduced specific N-uptake rates.
Key words
Free-air ozone fumigation - δ15 N - total N - net N-uptake - ectomycorrhiza.
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kristine.haberer@ctp.uni-freiburg.de
Guest Editor: R. Matyssek
