TY - JOUR

T1 - Fate of airborne nitrogen in heathland ecosystems a - 15N tracer study

AU - Friedrich, Uta

AU - Falk, Kirsten

AU - Bahlmann, Enno

AU - Marquardt, Thorben

AU - Meyer, Hartmut

AU - Niemeyer, Thomas

AU - Schemmel, Siegfried

AU - Oheimb, Goddert

AU - Härdtle, Werner

PY - 2011/4

Y1 - 2011/4

N2 - 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 the second year). Low 15N 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.

AB - 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 the second year). Low 15N 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.

KW - Biology

KW - Calluna vulgaris

KW - dry lowland heath

KW - N cycling

KW - N deposition

KW - N retention

KW - N saturation

KW - Ecosystems Research

UR - http://www.scopus.com/inward/record.url?scp=79952063676&partnerID=8YFLogxK

U2 - 10.1111/j.1365-2486.2010.02322.x

DO - 10.1111/j.1365-2486.2010.02322.x

M3 - Journal articles

VL - 17

SP - 1549

EP - 1559

JO - Global Change Biology

JF - Global Change Biology

SN - 1354-1013

IS - 4

ER -