Organic matter from biological soil crusts induces the initial formation of sandy temperate soils

• Algae- and moss-dominated BSCs developed within only four years.
• Soil formation was only found under moss-dominated BSCs.
• BSC-derived OC was mainly composed of carbohydrate-C, alkyl C and N-alkyl C.
• The chemical composition of BSC-derived OC changed with aging of crusts.
• BSCs contained recently assimilated C and lignite-derived old C as shown by 14C ages.

Different development stages of algae-dominated and moss-dominated biological soil crusts (BSCs) were sampled on a natural sand dune (< 17 years old) and on an experimental sand dune (< 8 years old) along a catena, including gradients of vegetation cover, location on the slope, as well as composition and thickness of BSC organisms in northeastern Germany. The accumulation of BSC-derived organic carbon (OC) was determined for bulk materials and fractions less than 63 μm. The OC composition was characterized by solid-state 13C NMR spectroscopy and the carbohydrate-C signature. 14C contents were determined to assess the origin and dynamics of OC. From the radiocarbon contents, two OC pools were differentiated: recent BSC-derived and lignite-derived “old” OC. Downward movement of OC into the underlying substrate was found only under moss-dominated BSCs at the old sand dune. BSC-derived OC was mainly composed of carbohydrate-C and, to a lesser extent, alkyl C and N-alkyl C, with considerably higher contributions of alkyl C in the young dune, indicating differences in the composition of extracellular polymeric substances produced by the BSCs with age. This is consistent with higher proportions of water-soluble OC of moss-dominated BSCs at the old dune, which is leached in the underlying substrate and initiates soil formation. Because of the channeling effect of mosses, OC depth translocation along with suspended colloidal substances may contribute to OC accumulation in substrates.