Creating High-Resolution Maps of Leaf Water Isotopes Using IM-CRDS and IRMS Techniques

Since the development of isotope ratio infrared spectroscopy (IRIS), the applications of water isotope analysis have been increasing. Here, we present a new protocol to create high-resolution maps of leaf water isotopes 18O and 2H. We use the Picarro induction module (IM-CRDS) combined with an isotope analyzer (L2130-i) to sample up to 25 locations in one half of each leaf. Each sampling location corresponds to four samples (6 mm outside diameter punched-holes) punched next to each other. In the induction module, an induction coil heats a metal holder containing the leaf sample. The sample will release water vapor that is then sent to the isotope analyzer. The IM-CRDS allows us to significantly reduce the sample size and therefore increase the sample density, compared to the traditional cryogenic extraction method. Using spatial analysis tools, we create high-resolution spatial maps of each isotope as well as d-excess maps. The water in the second half of the leaf is extracted by cryogenic extraction and analyzed using both IRIS and isotope ratio mass spectroscopy. The isotopic composition of the extracted water is compared to the average composition calculated from the maps and used for calibration. We present applications of this protocol to the analysis of the spatio-temporal evolution of foliar uptake in Colocasia esculenta under laboratory conditions.