Uni-Bayreuth grafik-uni-bayreuth



Rhizoliths in loess – determination of the origin using organic geochemical methods

Martina Gocke1, Guido L.B. Wiesenberg1, Konstantin Pustovoytov2, Yakov Kuzyakov2
1 Agrarökosystemforschung, Universität Bayreuth
2 Institut für Bodenkunde und Standortslehre, Universität Hohenheim

P 4.6 in Climate change research

Pedogenic (secondary) CaCO3 is formed in isotopic equilibrium with soil CO2 released by root and rhizomicrobial respiration. Therefore, d13C of pedogenic CaCO3 reflects the photosynthetic pathway of the local vegetation and is used for paleoenvironmental reconstruction. Rhizoliths are a special form of pedogenic CaCO3 formed by encrustation of plant roots by secondary CaCO3. While the organic part of the root is mainly degraded during decomposition, secondary CaCO3 remains in the terrestrial sediments. Rhizoliths may occur in calcareous sediments. The aim of our study was to elucidate the origin of rhizoliths on a molecular level in combination with stable C isotopic composition of CaCO3 and Corg. Loess-derived rhizoliths and loess from SW Germany were analysed for δ13C of CaCO3 and Corg, as well as carboxylic acid (CA) composition. δ13C of rhizolith Corg (–25.1‰) indicates the C3 photosynthetic pathway of the vegetation present at rhizolith formation. CA composition of the rhizolith matter confirmed these results. The comparison of CA distribution patterns in loess and in rhizoliths disproved the prevalent opinion about rhizolith formation taking place during loess sedimentation: Loess yielded a combined signal from shoot and root biomass reflecting former steppe vegetation, which is in accordance with loess sedimentation during glacial periods. In contrast, CA composition of rhizoliths reflects a root signal from bush or tree vegetation. This suggests that roots entered the loess later under different climatic conditions and consequently derive from different vegetation.

last modified 2009-03-06