Xylem and phloem in petioles are coordinated with leaf gas exchange in
oaks with contrasting anatomical strategies depending on leaf habit
Abstract
As the single link between leaves and the rest of the plant, petioles
must develop conductive tissues according to the water influx and sugar
outflow of the leaf lamina. A scaling relationship between leaf area and
anatomical traits of xylem and phloem is expected to improve the
efficiency of these tissues. However, the different constraints
compromising the functionality of both tissues (e.g., risk of
cavitation) must not be disregarded. Additionally, plants present two
main leaf habits (deciduous and evergreen) that may have different
strategies to produce and package their petiole conduits to cope with
environmental restrictions. In this study, we explore, in a diverse
group of 33 oak species, the relationships between petiole anatomical
traits, leaf area, stomatal conductance and photosynthesis rate. Results
showed allometric scaling between anatomical structure of xylem and
phloem with leaf area. We also found how photosynthesis and stomatal
conductance at leaf-level are correlated with anatomical traits in the
petiole. Nonetheless, the main novelty is how oaks present a different
strategy depending on the leaf habit. Deciduous species tend to increase
their diameters to achieve a greater leaf-specific conductivity. By
contrast, evergreen oaks develop larger xylem conductive areas for a
given leaf area than deciduous ones. This trade-off between
safety-efficiency in petioles has never been attributed to the leaf
habit of the species.