Fate of airborne nitrogen in heathland ecosystems - a 15N tracer study

Uta Friedrich (1) , Kirsten Falk (2) , Enno Bahlmann (3) , Thorben Marquardt (2) , Hartmut Meyer (2) , Thomas Niemeyer (2) , Siegfried Schemmel (2) , Goddert von Oheimb (2) , Werner Härdtle (2)

1 Institute of Ecology and Environmental Chemistry
2 Institute of Ecology and Environmental Chemistry
3 Institute for Biogeochemistry and Marine Chemistry

In the present study we analyze the fate of airborne nitrogen in heathland ecosystems (NW Germany) by means of a 15N tracer experiment. Our objective was to quantify N sequestration and N allocation patterns in an ecosystem that is naturally limited by N, but that has been exposed to airborne N inputs exceeding critical loads for more than 3 decades. We hypothesized that the system has a tendency towards N saturation, which should be indicated by low N sequestration and high N leaching. We analyzed 15N partitioning (aboveground biomass and soil horizons) and investigated 15N leaching over 2 years following a 15N tracer pulse addition. 15N tracer recovery was 90% and 76% in the first and second year, respectively. Contrary to our expectations, more than 99% of the tracer recovered was sequestered in the biomass and soil, while leaching losses were < 0.05% after 2 years. Mosses were the most important short-term sink for 15N (64% recovery in the first year), followed by the organic layer. In the second year, the moss layer developed from a sink to a source (23% losses), and soil compartments were the most important sink (gains of 11.2% in 2008). Low 15N tracer recovery in the current year's shoots of Calluna vulgaris (< 2%) indicated minor availability of 15N tracer sequestered in the organic layer. N partitioning patterns showed that the investigated heaths still have conservative N cycling, even after several decades of high N loads. This finding is mainly attributable to the high immobilization capacities for N of podzols in soil compartments. In the long term, the podzol-A- and B-horizons in particular may immobilize considerable amounts of incoming N. Since N compounds of these horizons are not readily bio-available, podzols have a high potential to withdraw airborne N from the system's N cycle.

Mots clés: Life Sciences

Uta Friedrich, Kirsten Falk, Enno Bahlmann, Thorben Marquardt, Hartmut Meyer, et al.. Fate of airborne nitrogen in heathland ecosystems - a 15N tracer study. Global Change Biology, 2010, 17 (4), pp.1549. ⟨10.1111/j.1365-2486.2010.02322.x⟩. ⟨hal-00599526⟩