Carbon and hydrogen isotope variation of plant biomarkers in a plant-soil system

Stable carbon (delta C-13) and hydrogen (delta D) isotopic compositions of n-alkanes, anteiso-alkanes, n-alkanoic acids, n-atkanols, phytol and sterols in raw leaves of Acer argutum and Acer carpinifolium, their fallen leaves, mold and soils from a natural Acer forest were measured in order to: (1) understand isotopic variation of the plant biomarkers in a plant-soil system and (2) evaluate which biomarker is the most effective recorder of soil vegetation. Long-chain (> C-24) n-alkanes, n-alkanoic acids and n-alkanols are gradually enriched in C-13 up to 12.9 parts per thousand (average of 4.3 parts per thousand) and depleted in D up to 94 parts per thousand (average of 55 parts per thousand) from raw leaves to soils. However, anteiso-alkanes, phytol and sterols show little variation in both delta C-13 (<+/- 1%.) and delta D (<+/- 2%.) from raw leaves to soils. These isotope signatures in a plant-soil system indicate that isoprenoid plant biomarkers such as sterols in soils faithfully preserve the isotopic compositions of dominant higher plants growing on the soils without a diagenetic effect upon the isotopic compositions. In contrast, long-chain n-alkyl molecules in soils undergo specific isotopic modification during biodegradation associated with early diagenesis and/or a significant contribution from heterotrophic reworking. (c) 2006 Elsevier B.V. All rights reserved.