super(15)N abundance of surface soils, roots and mycorrhizas in profiles of European forest soils

• Published in: Oecologia 1996-10, Vol.108 (2), p.207-214
• Main Authors: Hoegberg, P, Hoegbom, L, Schinkel, H, Hoegberg, M, Johannisson, C, Wallmark, H
• Format: Article
• Language: English
• ISSN: 0029-8549

super(15)N natural abundances of soil total N, roots and mycorrhizas were studied in surface oil profiles in coniferous and broadleaved forests along a transect from central to northern Europe. Under conditions of N limitation in Sweden, there was an increase in delta super(15)N of soil total N of up to 9ppt from the uppermost horizon of the organic mor layer down to the upper 0-5 cm of the mineral soil. The delta super(15)N of roots was only slightly lower than that of soil total N in the upper organic horizon, but further down roots were up to 5ppt depleted under such conditions. In experimentally N-enriched forest in Sweden, i.e. in plots which have received an average of c. 100 kg N ha super(-1) year super(-1) for 20 years and which retain less than 50% of this added N in the stand and the soil down to 20 cm depth, and in some forests in central Europe, the increase in delta super(15)N with depth in soil total N was smaller. An increase in delta super(15)N of the surface soil was even observed on experimentally N-enriched plots, although other data suggest that the N fertilizer added was depleted in super(15)N. In such cases roots could be enriched in super(15)N relative to soil total N, suggesting that labelling of the surface soil is via the pathway: - available pools of N - plant N - litter N. Under N-limiting conditions roots of different species sampled from the same soil horizon showed similar delta super(15)N. By contrast, in experimentally N-enriched forest delta super(15)N of roots increased in the sequence: ericaceous dwarf shrubs