Decomposability and chemical composition of soil organic matter in a Canadian High Arctic polar semi-desert environment

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Watson, Danika
soil organic matter , permafrost , Arctic , permafrost carbon feedback , x-ray photoelectron spectroscopy , XPS , molecular diversity , SOM , decomposability , recalcitrance , composition , spectroscopy , Cape Bounty Arctic Watershed Observatory , Nunavut , polar semi-desert , quality , incubation , soil , active layer , CO2 , mineralization , carbon
Arctic warming is driving widespread permafrost thaw, which could generate a positive feedback leading to further warming and release of vast amounts of carbon dioxide (CO2) into the atmosphere. The rate at which CO2 is released from the active layer of permafrost depends in part on the decomposability of active layer soil organic matter (SOM), which is poorly understood, particularly for polar semi-desert environments. A better understanding of active layer SOM decomposability is needed to inform models and project future climate warming. In this study, the decomposability of SOM in polar semi-desert soils collected at the Cape Bounty Arctic Watershed Observatory (CBAWO) on Melville Island, NU, Canada, was assessed with a 100-day soil incubation experiment. The potential influences of vegetation, soil texture, and molecular diversity (determined using X-ray photoelectron spectroscopy (XPS) characterization) on SOM decomposability were investigated. This is the first study to date that reports molecular diversity for polar semi-desert soils. In sandy soils, organic carbon (OC) concentration, CO2 production (g/g OC), fast-decomposing carbon (C) pool size (C1) and slow C pool decomposition rate (kr) were all higher in vegetated areas than unvegetated areas (as was molecular diversity, although this result was non-significant). However, OC concentration and CO2 production did not differ between vegetated and unvegetated soils in more clay-rich polar semi-desert sites. This suggests that the amount of soil mixing may vary between sites, possibly in relation to the influence of soil texture on cryoturbation. So, vegetation cover alone should not be used to map SOM properties in the polar semi-desert. Soils with high molecular diversity produced more CO2 and had larger fast-decomposing C pools than soils with lower molecular diversity. Thus, molecular diversity could be a valuable tool for predicting future CO2 production from the active layer of permafrost.
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