Microstructural and biochemical diversity of forest soil organic surface layers revealed by density fractionation

摘要: Abstract Particularly on sites with shallow, nutrient-poor soils, forest soil organic surface layers (O layers) are important for the storage of plant-available nutrients and water, thus vitality productivity. O can contain up to 70 mass percent inorganic compounds (minerals) which may be spatially separated from or closely associated matter (SOM). layer SOM differ in biochemical properties resistance against mineralization, depending extent organo-mineral association. Moreover, type intensity SOM-mineral mixing conveys information about biological activity. Here, first time we present detailed density fractionation results distinguish constituents different chemical likely also degrees Additionally, characterized spatial association patterns fractions. We investigated samples Of (Oe) Oh (Oa) horizons temperate soils parent materials (basalt, gneiss, andesite, Pleistocene gravel, dolomite). The were distinguished into six fractions (ρ  1.6 g cm−3) by sequential treatment deionized H2O (ρ = 1.0 g cm−3), 1-propanol (ρ = 0.8 g cm−3), sodium polytungstate (SPT) solution increasing (ρ = 1.2, 1.4, 1.6 g cm−3). procedure is a recovery 93 ± 5% an carbon (OC) 90 ± 9%. In each fraction, analyzed concentrations C, N, metal cations (Fe, Al, Ca, Mg), C speciation (13C NMR spectroscopy), as well abundances 13C 15N. For selected fractions, additionally determined radiocarbon age acquired microscopic images. From horizons, contribution heavy (>1.4 g cm−3) total SOC increased, indicating augmented organo–mineral progressive decomposition state. Compared bulk soil, heavier >1.4 g cm−3 smaller concentrations, whereas Al Fe increased >1.6 g cm−3 horizon. was enriched carboxyl alkyl but depleted O/N-alkyl aryl C. Smaller mean particle sizes C/N ratios / 15N indicate advanced state enrichment microbial-derived However, according its 14C signature, contrast high-density (ρ > 1.6 g cm−3) mineral floor high rapidly cycling pool turnover