Small-scale spatial patterns of soil organic carbon and nitrogen stocks in permafrost-affected soils of northern Siberia

At deeper permafrost table, SOC and N stocks (0-30 cm) were lower and, according to the semivariogram analysis, an overall homogenization of SOC and N distribution at the analyzed scale occurred. Total N and SOC stocks were spatially independent from root-derived organic matter distribution (i.e. the concentration of suberin-derived monomers) at shallow AL patches, whereas there was a significant positive spatial correlation within deep AL and non-permafrost soils. Hence, the development of root systems and an increase in rooting depth, leading to “hot spots” of SOM accumulation at intensively rooted soil patches, was observed as a result of deeper AL. Total N and SOC stocks within deeper AL and non-permafrost subsoils were also positively spatially correlated with the concentration of Fe and Al hydroxides, demonstrating the importance of organo-mineral associations for SOM stabilization in soils with lower permafrost table. This study confirmed that deepening of the AL in boreal forest ecosystems may lead to an overall homogenization of SOM distribution and simultaneous development of distinct mechanisms of SOM accumulation and stabilization.