Quantifizierung von postsedimentärem wurzelbürtigen Kohlenstoff in Löss mit molekularen Proxies zur Präzisierung von Paläoumweltrekonstruktionen
Zusammenfassung der Projektergebnisse
Terrestrial sedimentary archives such as loess-paleosol sequences became of increasing interest during the past decades as they enable paleoenvironmental investigations in situ, whereas marine and lacustrine archives provide integrated paleoenvironmental signals covering a whole catchment. The concept of sedimentary chronicity has been applied to loess-paleosol sequences, although frequently in profile descriptions roots and calcified root remains like rhizoliths and pseudomycelia have been mentioned. The project aimed to quantify, to which degree such archives are prone to postsedimentary alteration in the vicinity of roots and what this implies for paleoenvironmental reconstructions. Further, a model should be developed allowing for the correction of paleoenvironmental reconstruction that is necessary due to root- and rhizomicrobial overprint of organic matter composition in the respective archives. Several loess-paleosol sequences of different ages and terrestrial dune sands have been sampled along a transect from Nussloch (SW Germany), via Sopron and Katymar (Hungary), towards Irig and Šušara (Serbia). In all of the profiles abundances of recent roots, biopores and rhizoliths have been counted on horizontal levels, which for the first time led to an assessment of the spatial distribution of root features in terrestrial archives. Maximum abundances of 2100 m^-2, 4100 m^-2, 196 m^-2 and 12,800 m^-2 for roots, biopores, rhizoliths and microrhizoliths highlight the significance of rooting in terrestrial archives, which subsequently entails uncertainties in terms of source assessment of and thus paleoenvironmental reconstruction based on organic matter. Root counting and sampling was performed at all sites in depth increments of 0.1 – 0.2 m and three replicate samples per layer taken in areas without any or with lowest possible quantities of visible root remains. Further, undisturbed sediment and soil cores (with 0.20 – 0.25 m diameter) were taken with rhizoliths or roots located in their center. These cores enabled destructive sampling of the rhizosphere in the laboratory in concentric slices surrounding the roots and rhizoliths. For the first time, the rhizosphere analysis of rhizoliths enabled tracing of rhizosphere processes in distances of several cm surrounding the roots, which was assessed by carbon concentrations as well as various lipid biomarkers such as alkanes, fatty acids and glycerol dialkyl glycerol tetraethers. Microtomographic scans of undisturbed sediment cores showed that these large rhizosphere extensions are related to the presence of biopores that were produced by fine roots and remained as connected pore systems, as well as small rhizoliths (microrhizoliths), both of which are hardly assessable under field conditions. Further, the biogenic nature of the latter was demonstrated by microtomography, disproving the common assumption of their inorganic precipitation, as implied by the frequently used term ‘pseudomycelia‘. We therefore proposed to use the term ’microrhizoliths’ in future studies. Meanwhile, these findings became more and more acknowledged in the literature, although especially the significance of root- and rhizomicrobial-derived organic matter for lipid research and paleoenvironmental reconstruction is still under debate and has led to intensive scientific debates. Finally, the age of rhizoliths at the Nussloch site revealed their formation at different phases during the Holocene, while sedimentation took place during the Pleistocene. The strong variability of overprint of sedimentary organic matter in terms of quantity and quality further demands for correction of the reconstruction, which is currently under progress in several follow-up projects.
Projektbezogene Publikationen (Auswahl)
- 2012. Branched tetraether membrane lipids associated with rhizoliths in loess: rhizomicrobial overprinting of initial biomarker record. Organic Geochemistry 43, 12-19
Huguet A., Wiesenberg G.L.B., Gocke M., Fosse C., Derenne S.
(Siehe online unter https://doi.org/10.1016/j.orggeochem.2011.11.006) - 2013. Differentiation of plant derived organic matter in soil, loess and rhizoliths based on n-alkane molecular proxies. Biogeochemistry 112, 23-40
Gocke M., Kuzyakov Y., Wiesenberg G.L.B.
- 2013. Root-associated tetraether source microorganisms may reduce estimated paleotemperatures in subsoil. Chemical Geology 356, 1-10
Huguet A., Gocke M., Derenne S., Fosse C., Wiesenberg G.L.B.
(Siehe online unter https://doi.org/10.1016/j.chemgeo.2013.07.017) - 2014. Biopores and root features as new tools for improving paleoecological understanding of terrestrial sediment-paleosol sequences. Palaeogeography, Palaeoclimatology, Palaeoecology 394, 42-58
Gocke M., Gulyás S., Hambach U., Jovanović M., Kovács G., Marković S.B., Wiesenberg G.L.B.
(Siehe online unter https://doi.org/10.1016/j.palaeo.2013.11.010) - 2014. Introducing an improved multi-proxy approach for paleoenvironmental reconstruction of loess–paleosol archives applied on the Late Pleistocene Nussloch sequence (SW Germany). Palaeogeography, Palaeoclimatology, Palaeoecology 410, 300-315
Gocke M., Hambach U., Eckmeier E., Schwark L., Zöller L., Fuchs M., Löscher M., Wiesenberg G.L.B.
(Siehe online unter https://doi.org/10.1016/j.palaeo.2014.06.006) - 2014. Lateral and depth variation of loess organic matter overprint related to rhizoliths. Catena 112, 72-85
Gocke M., Peth S., Wiesenberg G.L.B.
(Siehe online unter https://doi.org/10.1016/j.catena.2012.11.011)
