Conclusions
Cell wall and other anatomical properties can affect Δ18OLW by manipulating Ethrough altering water flow along the transpiration stream andL v through altering water channeling out of the xylem and to the stomata. This influence is apparent in variation in Δ18OLW between C3 and C4 grass species that can be attributed to differences in vasculature that limit water flow out of the vasculature in C4 species and may be an indication of differing hydraulic attributes. Studying the interactions of anatomical features and physiological traits in water movement through and outside of the xylem can shed more light on Δ18OLWbecause either physiology or anatomy alone fails to capture the isotopic implications of water movement. Consequently, stable isotopes can be used to study this interaction. With the development of gene editing, Δ18OLW can potentially be used to better understand gene-phenotype relationships of traits related to water movement in the leaf. For example, when studying genes associated with Sd, differences in water movement may not be discernable from measures of Sd per se , but nevertheless differences in Sd can influence Δ18OLW and indicate a subtle response of Sd to genotype or environmental conditions. Further integration between leaf water transport through and outside the xylem with stable isotope theory will facilitate the development of a physiologically and anatomically explicit water transport model.