| Summary: | Over the past millennia, complex terrestrial ecosystems have evolved in the Arctic. However, the stability of these unique ecosystems is in jeopardy because of climate changes. Due to the fact that Arctic soils store great amounts of carbon (C) in soil organic matter (SOM), any change that may occur in SOM with climate changes may substantially affect many aspects of Arctic ecosystems such as vegetation, animals, and humans. On a more global perspective, any change in Arctic SOM has the potential of modifying the overall world climate by affecting the global greenhouse gas (GHG) budget. A better understanding of the soil factors that affect soil N and C cycling at the landscape scale, such as moisture, temperature, and SOM characteristics, is necessary to produce better models. The overall objective of this study was to characterize the properties of SOM in Arctic soils and their influence on soil N and C cycling dynamics - including GHG emissions - at the landscape scale. This study was conducted in three distinct Arctic ecosystems: Sub-Arctic (Churchill, MB), Low-Arctic (Daring Lake, NWT), and High-Arctic (Truelove, NU). For each site, the sampling locations were evenly divided into five landform units: 1) upper slope (Up), 2) back slope (Back), and 3) lower slope (Low) for catena sites, and 4) hummock (Hum) and 5) wedges of hummock (W) for hummocky sites (i.e., hummock in Churchill and ice-wedge polygons in Truelove). All sites were sampled at the end of their growing season (from 2 to 3 weeks before plant senescence). The characteristics of SOM were assessed using three methods: 1) density fractionation to separate the uncomplexed light fraction (LF) from heavy fraction (HF) of SOM (LF < 1.55 g mL⁻¹ < HF), 2) solid-state CPMAS ¹³C nuclear magnetic resonance (NMR) spectroscopy that determined the relative proportions of carbonyl-C (CbyC), alkyl-C (AC), aromatic-C (AroC), o-alkyl-C (OAC), and carbohydrates-C (CC), and 3) water-extractable organic matter (WEOM) that estimated SOM diluted in soil solution. ...
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