Where ϕx is the fraction of leaf water in the xylem, and
Pr and Pm are the xylem and mesophyll
Péclet numbers, respectively. This model allows for different Péclet
effects in each tissue type (Gan et
al. 2003; Holloway-Phillips et
al. 2016). The influence of the xylem Péclet depends on physiological
traits such as E that regulates flow velocity and anatomical
traits, such as vein density, fraction vein volume, stomatal density and
size, and specific water content
(Sternberg & Manganiello 2014;
Larcher et al. 2015;
Song et al. 2015;
Holloway-Phillips et al. 2016;
Liang et al. 2018). Potentially
multiple other anatomical traits that influence the movement of water
along the transpiration pathway and in the leaf alter
Δ18OLW. The Farquhar-Gan model can be
modified by excluding the mesophyll Péclet if it is small or nonexistent
compared to xylem Péclet (Eqn. 11). Therefore, the Péclet effect