We report the first simultaneous measurements of ?15N and ?13C of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The ?13C and ?15N of DNA was correlated with ?13C and ?15N of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in 13C relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used 13C enriched substrates. Enrichment of DNA in 15N relative to soil was not consistently observed, but there were significant differences between ?15N of DNA and ?15N of soil for three different sites, suggesting [...]
