『Abstract
Arctic soils store great amounts of soil organic matter (SOM)
that are likely to be affected by future climate changes. Knowledge
of the ability of the soil to mineralize nitrogen (N) and release
greenhouse gases (GHG) at the landscape scale is critical to predict
and model future effects of climate change on Arctic SOM. The
objective of this study was to investigate how soil gross N mineralization
and GHG emissions vary across landscapes and Arctic ecosystems.
This study was conducted in three Arctic systems: Sub-Arctic (Churchill,
MB), Low-Arctic (Daring Lake, NWT), and High-Arctic (Truelove
Lowlands, NU). The topography was divided into five landform units:
1) upper (Up), 2) back (Back), and 3) lower (Low) slopes for catena
sites and 4) hummock and 5) interhummock for hummocky sites (i.e.,
hummock in Churchill and ice-wedge polygons in Truelove). All
sites were sampled near the end of their growing seasons (i.e.,
from two to three weeks before plant senescence). Soil gross N
mineralization was measured in situ using a 15N dilution
technique, whereas soil GHG emissions (N2O,
CH4, and CO2) were measured
in situ using a multicomponent Fourier transform infrared gas
analyzer combined with an automated dark chamber. Foe all ecosystems,
topography significantly influenced soil gross N mineralization
and CO2 emissions. Topography had no significant
impact on N2O and CH4
fluxes most likely because net fluxes were extremely low throughout
landscapes. Soil gross N mineralization and CO2
emissions increased from Up, Back, to Low and from hummock to
interhummock landform units. Foe example, at Churchill, soil gross
mineralization rates averaged 4 mg N-NH4+
kg-1 d-1 in upper slopes and progressively
increased to about 25 mg N-NH4+
kg-1 d-1 in the lower slopes. Similarly,
CO2 emission rates at Daring Lake averaged
0.5μmol CO2 m-2 s-1
in upper slopes and progressively increased to about 2.3μmol CO2 m-2 s-1 in the lower slopes.
Comparisons among ecosystems showed that Churchill (Sub-Arctic)
had the highest gross N mineralization rates followed by Truelove
(High-Arctic) and Daring Lake (Low-Arctic). Furthermore, Daring
Lake had significantly higher CO2 emissions
than Churchill and no difference in CH4 and
N2O emissions between both ecosystems was
found. These findings suggest that all factors influencing C and
N cycling processes such as climate and human induced changes
may not have similar effects across landscapes or across Arctic
ecosystems.
Keywords: Nutrient cycling; Gross N mineralization; Arctic; Tundra』
1. Introduction
2. Material and methods
2.1. Study locations
2.1.1. Sub-Arctic: Churchill
2.1.2. Low-Arctic: Daring Lake
2.1.3. High-Arctic: Truelove
2.2. Method of sampling
2.3. Soil general analysis
2.4. Soil N mineralization
2.5. Soil GHG emissions
2.6. Statistical analysis
3. Results and discussion
3.1. Soil gross N mineralization and topography
3.2. Soil GHG emissions and topography
3.2.1. N2O emissions
3.2.2. CH4 emissions
3.2.3. CO2 emissions
3.3. Ecosystem comparisons
3.4. Changing climate: a landscape perspective
3.4.1. Integrating N mineralization and GHG emissions
3.4.2. Soil temperature paradigm
4. Conclusions
Acknowledgments
References