© 2001 Heron Publishing—Victoria, Canada
Fate of nitrogen released from 15N-labeled litter in European beech forests
Bernd Zeller (1), Micheline Colin-Belgrand (1), Etienne Dambrine (1) and Francis Martin (2)
1. Équipe Cycles Biogéochimiques, INRA Centre de Nancy, 54280 Champenoux, France / 2. Équipe Microbiologie Forestière, INRA Centre de Nancy, 54280 Champenoux, France / Received December 7, 1999
Summary
The decomposition and fate of 15N-labeled beech litter was monitored in three European beech (Fagus sylvatica L.) forests (Aubure, France; Ebrach, Germany; and Collelongo, Italy) for 3 years. Circular plots around single beech trees
were isolated from roots of neighboring trees by soil trenching, and annual litterfall was replaced by 15N-labeled litter. Nitrogen was continuously released from the decomposing litter. However, over a 2-year period, this release
was balanced by the incorporation of exogenous N. Released N accumulated mainly at the soil surface and in the topsoil. Microbial
biomass remained almost constant during the experiment at all sites except for considerably lower values at Ebrach. The 15N enrichment of the microbial biomass increased strongly during the first year and then remained stable. The 15N released from the decomposing litter was rapidly detected in roots and leaves of the beech trees, increasing regularly and
linearly over the course of the experiment. The uptake of litter-released 15N by the trees was reduced under conditions that reduced tree growth. Under these conditions, leaves and fine roots were the
dominant N sinks, and little N was allocated to other plant parts. By contrast, N uptake and N allocation from leaves to stem
and bark tissues increased when tree growth was enhanced. Budgets for 15N showed that 2 to 4% of litter-released N was incorporated into the trees, about 35% remained in the litter and about 50%
reached the topsoil.
Keywords:
Fagus sylvatica, litter decomposition, N cycle, nitrogen, N partitioning, N uptake.
