Stability and biodegradability of humic substances from Arctic soils of Western Siberia: insights from ¹³C-NMR spectroscopy and elemental analysis

Abstract

Abstract. 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 emphasize 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 solid-state 13C-NMR spectroscopy. Also, the total mineralisable carbon was measured. Our results show that there is a uniformity of SOM characteristics throughout the studied region, as well as within soil profiles. Such in-depth homogeneity, together with a predominance of aliphatic carbon structures, suggests the accumulation in soil of raw and slightly decomposed organic matter. Moreover, results on total mineralisable carbon suggest a high lability of these compounds. The mineralisation rate was 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 fundamental role that the soils of Western Siberia may have on regulating the global carbon balance when faced with increasing ambient temperatures.