Spatial Variability of the Stocks of Different Organic Carbon Compounds in a Leptic Cambisol Under Norway Spruce.

Soil organic carbon (OC) stocks of forest soils are known to be characterized by high variability at small scales. The variability of different OC fractions (HF-soluble OC fraction, representing mineral associated OC and HF-resistant OC fraction, representing the non-mineral associated OC), different OC compounds (lignin phenols, non-cellulosic neutral sugars) and their relation to site specific factors (e.g. bulk density, pH and content of oxalate extractable iron and aluminum oxides), however, is largely unknown.

We studied a dystric, laxic Leptic Cambisol site (900 m²) stocked with Norway spruce in the Nationalpark Bayerischer Wald. Soil samples were taken at the nodes of a rectangular grid with distances of 5 m and a nested sampling scheme with a sampling distance of 0.2 m. Comparison of the HF-soluble and the non-soluble OC stocks showed that only the HF-soluble OC stock exhibited a spatial pattern. In contrast, the non-soluble OC stocks were characterized by a pure nugget effect. HF-soluble stocks of neutral sugars were significantly spatially correlated with the pH and the amount of oxalate extractable iron and aluminum oxides in both horizons. Comparison of the spatial variability of the different OC species of the HF-soluble OC showed an increasing spatial variability in the order aryl C < carboxyl C < alkyl C < O/N-alkyl C.

Our results indicate that the spatial variability of OC stocks is mainly due to the spatial variability of the HF-soluble OC stocks. Different spatial distribution patterns of different OC species indicate different stabilization mechanisms.