Carbon stable isotope composition of DNA isolated from an incipient paleosol

We determined the carbon isotope (δ¹³C) value of double-stranded DNA (dsDNA) isolated from the organic horizons of a Delaware soil that is actively being covered by an encroaching sand dune. The soil belongs to a Nymphaea odorata Ait. (water lily) wetland, and we regard its active acquisition of a thick (∼24 cm) surface mantle to embody the process of paleopedogenesis; therefore, we have termed it an "incipient paleosol." In this study, we compared the δ¹³C value of paleosol dsDNA to the bulk δ ¹³C value of N. odorata, as well as to the δ ¹³C value of plants that had colonized the surface mantle. The isotopic offset between paleosol δ¹³C_dsDNA and N. odorata δ¹³C_tissue was identical to the relationship between δ¹³C_dsDNA and δ¹³C_tissue for tracheophytes, which we had previously determined. In contrast, the isotopic offset between paleosol δ¹³C_dsDNA and the δ¹³C_tissue of plants colonizing the surface mantle differed from this relationship by as much as 4‰. Similarly, the δ¹³C value of bulk paleosol organic matter was extremely heterogeneous and varied across 6‰. All paleosol DNA polymerase chain reaction (PCR) products produced clear, sharp, 350 base-pair (bp) fragments of rbcL, a gene shared by all photosynthetic organisms. These results open the exciting possibility that stable isotope analysis of dsDNA isolated from paleosol organic matter can be used to infer the δ¹³C value of the plant that dominated the nucleic acid contribution.