Stability and biodegradability of organic matter from Arctic soils ofWestern Siberia: insights from 13C-NMR spectroscopy and elemental analysis

Arctic soils contain large amounts of organic matter which, globally, exceed the amount of carbon stored in vegetation biomass and in the atmosphere. Recent studies emphasise the potential sensitivity for this soil organic matter (SOM) to be mineralised when faced with increasing ambient temperatures. In order to better refine the predictions about the response of SOM to climate warming, there is a need to increase the spatial coverage of empirical data on SOM quantity and quality in the Arctic area. This study provides, for the first time, a characterisation of SOM from the Gydan Peninsula in the Yamal Region,Western Siberia, Russia. On the one hand, soil humic acids and their humification state were characterised by measuring the elemental composition and diversity of functional groups using solidstate 13C-nuclear magnetic resonance (NMR) spectroscopy. Also, the total mineralisable carbon was measured. Our results indicate that there is a predominance of aliphatic carbon structures, with a minimal variation of their functional-group composition both regionally and within soil depth. This vertical homogeneity and low level of aromaticity reflects the accumulation in soil of lowly decomposed organic matter due to cold temperatures. Mineralisation rates were found to be independent of SOM quality, and to be mainly explained solely by the total carbon content. Overall, our results provide further evidence on the sensitivity that the soils ofWestern Siberia may have to increasing ambient temperatures and highlight the important role that this region can play in the global carbon balance under the effects of climate warming.This study was supported by the Russian president grant for Young Doctors of Science “Complex investigation of soil diversity and ecological functions of Northern part of Western Siberia on example of Yamal and Gydan peninsula” (MD 3615- 2015-4), as well as by the Russian Foundation for Basic Research project for young doctors and candidates of sciences (16-34-60010). Analytical analyses were performed at the Centre for Magnetic Resonance and at the Centre for Chemical Analysis and Materials Research of Research Park of St Petersburg State University