Botanical isoscapes: emerging stable isotope tools for geographic sourcing and authentication

The global hydrologic cycle generates predictable, spatially coherent variation in the stable hydrogen and oxygen isotopes of water (δ²H and δ¹⁸O) at local to global scales. This includes variation in precipitation along such spatial gradients as latitude and elevation. Because plants use water from soils that are recharged by precipitation or irrigation and the H and O from this water is incorporated into the organic molecules of plant tissues, there is the potential to use plant δ²H and δ¹⁸O for geographic assignment and authentication. We know that plant tissues “record” the isotopic composition of soil water, but with some important modifications. The local water signal is altered by evaporative losses from leaves (transpiration) and the biochemical processes associated with plant growth. Recent advances in modeling these process, as well as technological developments accelerating the accumulation of data on plant δ²H and δ¹⁸O have opened up new avenues of research and potential tools for authentication. I will present areas where we have modeled and mapped the spatial variation of plant-derived products, including such diverse products as wine and the drug of abuse marijuana. I will also discuss new tools that we have developed and made available online (http://isomap.org) to allow spatial modeling of stable isotopes, the generation of maps of this variation (isoscapes¹), and statistically rigorous geographic assignment. Finally, I will discuss areas that are likely to be productive avenues for future research in geographic origin identification and authentication.

Fig.1: Global Leaf Water Isoscape

Reference:

¹ West, JB, GJ Bowen, TE Dawson, KP Tu. 2010. Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping, 487 pgs. Springer, Dordrecht. ISBN 978–90–481–3353–6.