TY - JOUR

T1 - Nitrogen fixation, denitrification, and ecosystem nitrogen pools in relation to vegetation development in the Subarctic

AU - Sørensen, Pernille Lærkedal

AU - Jonasson, Sven Evert

AU - Michelsen, Anders

PY - 2006

Y1 - 2006

N2 - Nitrogen (N) fixation, denitrification, and ecosystem pools of nitrogen were measuredin three subarctic ecosystem types differing in soil frost-heaving activity and vegetationcover. N2-fixation was measured by the acetylene reduction assay and converted toabsolute N ecosystem input by estimates of conversion factors between acetylenereduction and 15N incorporation. One aim was to relate nitrogen fluxes and nitrogen poolsto the mosaic of ecosystem types of different stability common in areas of soil frostmovements. A second aim was to identify abiotic controls on N2-fixation by simultaneousmeasurements of temperature, light, and soil moisture.Nitrogen fixation rate was high with seasonal input estimated at 1.1 g N m2 on frostheavedsorted circles, which was higher than the total plant N content and exceededestimated annual plant N uptake several-fold but was lower than the microbial N content.Seasonal fixation decreased to 0.88 g N m2 on frost-heaved moss-covered surfaces and to0.25 g N m2 in stable heath vegetation, both lower than the plant and microbial N content.Yet fixation was estimated to correspond to about 2.7 times the annual plant N demandon the moss-covered surfaces but less than the plants' demand on the heath. Surprisingly,we found no denitrification on any surface.Climatic changes in the Arctic will generate a warmer climate and changeprecipitation patterns. A warmer, drier environment will decrease N2-fixation and therebyN availability to plants and microorganisms, while wetter conditions probably will increaseN2-fixation and thereby N supply to the surroundings.

AB - Nitrogen (N) fixation, denitrification, and ecosystem pools of nitrogen were measuredin three subarctic ecosystem types differing in soil frost-heaving activity and vegetationcover. N2-fixation was measured by the acetylene reduction assay and converted toabsolute N ecosystem input by estimates of conversion factors between acetylenereduction and 15N incorporation. One aim was to relate nitrogen fluxes and nitrogen poolsto the mosaic of ecosystem types of different stability common in areas of soil frostmovements. A second aim was to identify abiotic controls on N2-fixation by simultaneousmeasurements of temperature, light, and soil moisture.Nitrogen fixation rate was high with seasonal input estimated at 1.1 g N m2 on frostheavedsorted circles, which was higher than the total plant N content and exceededestimated annual plant N uptake several-fold but was lower than the microbial N content.Seasonal fixation decreased to 0.88 g N m2 on frost-heaved moss-covered surfaces and to0.25 g N m2 in stable heath vegetation, both lower than the plant and microbial N content.Yet fixation was estimated to correspond to about 2.7 times the annual plant N demandon the moss-covered surfaces but less than the plants' demand on the heath. Surprisingly,we found no denitrification on any surface.Climatic changes in the Arctic will generate a warmer climate and changeprecipitation patterns. A warmer, drier environment will decrease N2-fixation and therebyN availability to plants and microorganisms, while wetter conditions probably will increaseN2-fixation and thereby N supply to the surroundings.

U2 - 10.1657/1523-0430(2006)38[263:NFDAEN]2.0.CO;2

DO - 10.1657/1523-0430(2006)38[263:NFDAEN]2.0.CO;2

M3 - Journal article

VL - 38

SP - 263

EP - 272

JO - Arctic, Antarctic, and Alpine Research

JF - Arctic, Antarctic, and Alpine Research

SN - 1523-0430

IS - 2

ER -