L is the product of two components related to leaf anatomy: one
that accounts for the tortuosity of water pathway from the xylem to the
stomatal pore (l ) and the other refers to the cross-sectional
area perpendicular to water flow relative to the leaf surface area
(k ) (Barbour & Farquhar 2004;
Cernusak & Kahmen 2013;
Song et al. 2013;
Sternberg & Manganiello 2014). The
assumption that L is constant for species, across treatments, and
across a gradient of transpiration rates has not always been supported
(Song et al. 2013;
Roden et al. 2015). The lack of
understanding of L and the factors that affect it largely arise
from the difficulty of measuring L .
The determining evidence of the presence of the Péclet effect is if the
fractional contribution of source water (unenriched xylem water;f sw) increases with E (Eqn. 9;
Song et al. 2015;
Holloway-Phillips et al. 2016). A
Péclet effect has failed to be observed in several