A δ²H Isoscape of blackberry as an example application for determining the geographic origins of plant materials in New Zealand

In this investigation, two previously reported precipitation δ²H isoscapes for New Zealand were used to develop a δ²H isoscape for blackberry (Rubus sp.) leaf. These isoscapes were calibrated using the measured δ²H values of 120 authentic blackberry leaf samples collected from across the country. A regression model based on environmental variables available for New Zealand was also determined to predict δ²H values measured from blackberry leaves without initially modelling the precipitation δ²H values. The three models were compared for their accuracy and precision when assigning 10 samples of blackberry leaves for their geographic location based on their measured δ²H values. One of the models based on a precipitation isoscape was similar in accuracy and precision of assignment to the model determined from the environmental variables and provides an approach for determining valid isoscapes for future plant materials.