TY - JOUR

T1 - Fate of ammonium 15N in a Norway spruce forest under long-term reduction in atmospheric N deposition

AU - Dörr, Nicole

AU - Kaiser, Klaus

AU - Sauheitl, Leopold

AU - Lamersdorf, Norbert

AU - Stange, C. Florian

AU - Guggenberger, Georg

N1 - Funding information: Acknowledgments We are grateful to Dirk Böttger for the management of the experimental site and his help during the sampling. We thank Pieter Wiese and Bernd Apelt for laboratory assistance and Jeannette Boguhn for EA-IRMS measurements. The work was financial supported by the German Research Foundation (PAK 12, GU 406/14-1).

PY - 2010/12/15

Y1 - 2010/12/15

N2 - In the last decades, in particular forest ecosystems became increasingly N saturated due to elevated atmospheric N deposition, resulting from anthropogenic N emission. This led to serious consequences for the environment such as N leaching to the groundwater. Recent efforts to reduce N emissions raise the question if, and over what timescale, ecosystems recover to previous conditions. In order to study the effects on N distribution and N transformation processes under the lowered N deposition treatment, we investigated the fate of deposited NH4+-15N in soil of a N-saturated Norway spruce forest (current N deposition: 34 kg ha-1 year-1; critical N load: 14 kg ha-1 year-1), where N deposition has been reduced to 11. 5 kg ha-1 year-1 since 14. 5 years. We traced the deposited 15N in needle litter, bulk soil, and amino acids, microbial biomass and inorganic N in soil. Under reduced N deposition, 123 ± 23% of the deposited N was retained in bulk soil, while this was only 72 ± 15% under ambient deposition. We presume that with reduced deposition the amount of deposited N was small enough to become completely immobilized in plant and soil and no leaching losses occurred. Trees receiving reduced N deposition showed a decline in N content as well as in 15N incorporation into needle litter, indicating reduced N plant uptake. In contrast, the distribution of 15N within the soil over active microbial biomass, microbial residues and inorganic N was not affected by the reduced N deposition. We conclude that the reduction in N deposition impacted only plant uptake and drainage losses, while microbial N transformation processes were not influenced. We assume changes in the biological N turnover to start with the onset of the decomposition of the new, N-depleted litter.

AB - In the last decades, in particular forest ecosystems became increasingly N saturated due to elevated atmospheric N deposition, resulting from anthropogenic N emission. This led to serious consequences for the environment such as N leaching to the groundwater. Recent efforts to reduce N emissions raise the question if, and over what timescale, ecosystems recover to previous conditions. In order to study the effects on N distribution and N transformation processes under the lowered N deposition treatment, we investigated the fate of deposited NH4+-15N in soil of a N-saturated Norway spruce forest (current N deposition: 34 kg ha-1 year-1; critical N load: 14 kg ha-1 year-1), where N deposition has been reduced to 11. 5 kg ha-1 year-1 since 14. 5 years. We traced the deposited 15N in needle litter, bulk soil, and amino acids, microbial biomass and inorganic N in soil. Under reduced N deposition, 123 ± 23% of the deposited N was retained in bulk soil, while this was only 72 ± 15% under ambient deposition. We presume that with reduced deposition the amount of deposited N was small enough to become completely immobilized in plant and soil and no leaching losses occurred. Trees receiving reduced N deposition showed a decline in N content as well as in 15N incorporation into needle litter, indicating reduced N plant uptake. In contrast, the distribution of 15N within the soil over active microbial biomass, microbial residues and inorganic N was not affected by the reduced N deposition. We conclude that the reduction in N deposition impacted only plant uptake and drainage losses, while microbial N transformation processes were not influenced. We assume changes in the biological N turnover to start with the onset of the decomposition of the new, N-depleted litter.

KW - N tracer

KW - Amino acids

KW - Microbial biomass

KW - N deposition

KW - Solling roof project

UR - http://www.scopus.com/inward/record.url?scp=83555177631&partnerID=8YFLogxK

U2 - 10.1007/s10533-010-9561-z

DO - 10.1007/s10533-010-9561-z

M3 - Article

AN - SCOPUS:83555177631

VL - 107

SP - 409

EP - 422

JO - BIOGEOCHEMISTRY

JF - BIOGEOCHEMISTRY

SN - 0168-2563

IS - 1-3

ER -