The effect of water availability on the carbon and nitrogen isotope composition of a C4 plant (pearl millet, Pennisetum glaucum)

•Pearl millet δ13C values are positively correlated with water availability.•Regional origin influences pearl millet carbon isotope ratios to a similar degree.•Past water status cannot be reconstructed from pearl millet δ13C values alone.•Pearl millet δ15N values did not differ among water treatments.