Landscape-Scale Organic Matter Mineralization in Canadian Arctic Gelisols.

Permafrost-affected soils store a large quantity (~16% of the world’s soil carbon) of soil organic matter (SOM). Warmer temperature trends throughout Arctic Canada are changing this reality. Therefore, studying parameters that influence SOM mineralization is fundamental to predict global warming feedbacks on both SOM balance and plant communities. The objectives of this study were to investigate the influence of soil moisture gradient on 1) SOM mineralization and 2) other soil attributes influencing SOM mineralization. This study was conducted in three distinct Canadian Arctic ecosystems: High-Arctic (Truelove Lowlands, NU), Low-Arctic (Daring Lake, NWT), and Sub-Arctic (Churchill, MB). The sampling locations were distributed along two common Arctic landscape features: 1) Gelisolic catena (Upper slope; Back slope; Lower slope) and 2) Peat hummock system (Hummock center; Wedge of hummock). Truelove Lowlands (n=54) and Daring Lake (n=60) were sampled in 2008 and Churchill (n=138) was sampled in 2009. All sites were sampled at the end of their growing seasons (~2 to 3 weeks before plant senescence). Organic matter mineralization was measured using two field-based methods: 1) net soil surface carbon dioxide (CO₂) emissions using a multicomponent fourier transform infrared (FTIR) gas analyzer combined with an automated dark chamber; and 2) soil gross N mineralization determination using ¹⁵NH₄⁺ dilution technique. Other soil attributes that might influence SOM mineralization (i.e., temperature; pH; water-extractable dissolved organic N (DON) and carbon (DOC); solid SOM density fractions (light fraction < 1.55 g ml^-1 < heavy fraction); relative content of Alkyl-C, O-Alkyl-C, Carbohydrates, Aromatic-C, and Carbonyl) were also measured on each location. Results and their implications will be discussed.