Abstract
Leaf stomatal density is known to covary with leaf vein density.
However, the functional underpinning of this relation, and how it scales
to whole-plant water transport anatomy, is still unresolved. We
hypothesized that the balance of water exchange between the vapour phase
(in stomata) and liquid phase (in vessels) depends on the consistent
scaling between the summed stomatal areas and xylem cross-sectional
areas, both at the whole-plant and single-leaf level. This predicted
size-covariation should be driven by the covariation of numbers of
stomata and terminal vessels. We examined the relationships of stomatal
traits and xylem anatomical traits from the entire plant to individual
leaves across seedlings of 53 European woody angiosperm species. There
was strong and convergent scaling between total stomatal area and stem
xylem area per plant and between leaf total stomatal area and midvein
xylem area per leaf across all the species, irrespective of variation in
leaf habit, growth-form or relative growth rate (RGR). Moreover, strong
scaling was found between stomatal number and terminal vessel number
while not in their respective average areas. Our findings have broad
implications for integrating xylem architecture and stomatal
distribution, and deepen our understanding of the design rules of
plants’ water transport network.