Biogeochemical and ecological responses to warming climate in High Arctic polar deserts

Abstract

High Arctic polar deserts cover 26% of the Arctic and are found to store a larger amount of soil organic carbon (SOC) in the permafrost and to emit higher amounts of the main greenhouse gases (GHGs) than previously expected. However, the mechanisms of the main GHG production are not clear. Furthermore, polar deserts are predicted to dramatically transform under rapidly warming temperatures and have uncertainty regarding a potential positive GHG-feedback to the warming climate. Freeze-thaw cycles develop frost-boil landscape and diapirs within frost-boil profiles. Diapirs are cryoturbic nutrient patches and support vascular plants in polar deserts. Frost-boil development and diapirs are expected to increase with the increase in temperatures and the permafrost thaw and are likely key for projected polar-desert evolutions. This dissertation investigated soil properties including the chemical structure of SOC, microbial processes responsible for GHG emissions, and the main GHG emissions associated with diapirism. Diapirs had increased polysaccharides known to raise soil viscosity, which in turn facilitates diapirism. In addition to this, diapirs contained more recalcitrant SOC, which was consistent with the decreases in gross nitrogen mineralization by 30–48% and in carbon dioxide (CO2) emissions by 19–38%. Similarly, diapiric frost boils slowed net methane (CH4) emissions. With higher archaeal amoA abundance, diapiric frost boils had a higher magnitude of the emissions leading to a higher estimate of the emissions under dry conditions. On the other hand, a higher estimate of the emissions from diapiric frost boils linked to a higher probability of the emissions under wet conditions. Freeze-thaw treatment increased CO2 emissions by 1.3–3.5 times and estimation of N2O emissions by 72–204% but apparently reduced CH4 consumption more than CH4 production to increase net CH4 emissions. This dissertation found that diapirisms alter SOC components and the main GHG emissions. The higher abundance of polysaccharides and recalcitrant SOC suggests that biological factors are involved in diapirism and that diapirs supply vascular plants with nutrients as a result of a mutualistic relationship. Furthermore, this dissertation suggests that freeze-thaw triggers the main GHG emissions leading to the distinct emission patterns during snowmelt season from later growing season.