Rhizoliths in loess - evidence for post-sedimentary incorporation of root-derived organic matter in terrestrial sediments as assessed from molecular proxies

Loess OM gave a combined signal from shoot and root biomass from grass vegetation, confirming the assumption of deposition during glacial periods with scarce grass vegetation cover. In contrast, the lipid composition of rhizolith OM reflected roots of woody vegetation, indicating the post-sedimentary character of rhizoliths. Stronger degradation of OM, together with a large content of microorganism-derived FAs in the former rhizosphere indicated rhizodeposition associated with high microbial activity in loess adjacent to rhizoliths, at least up to a distance of 5 cm. Rhizosphere loess and reference loess at a distance of 50-70 cm showed a significantly different OM composition, thereby revealing the incorporation of considerable portions of root-derived OM into loess in the vicinity of roots. Further studies are necessary for an exact quantification of this potential overprint of the syn-sedimentary loess OM, which might cause uncertainty in palaeoenvironmental studies.