Axial anatomy of the leaf midrib provides new insights into the hydraulic architecture and cavitation patterns of Acer pseudoplatanus leaves

Abstract

The structure of leaf veins is typically described by a hierarchical scheme (e.g. midrib, 1st order, 2nd order), which is used to predict variation in conduit diameter from one order to another whilst overlooking possible variation within the same order. We examined whether xylem conduit diameter changes within the same vein order, with resulting consequences for resistance to embolism. We measured the hydraulic diameter (Dh), and number of vessels (VN) along the midrib and petioles of leaves of Acer pseudoplatanus, and estimated the leaf area supplied (Aleaf-sup) at different points of the midrib and how variation in anatomical traits affected embolism resistance. We found that Dh scales with distance from the midrib tip (path length, L) with a power of 0.42, and that VN scales with Aleaf-sup with a power of 0.66. Total conductive area scales isometrically with Aleaf-sup. Embolism events along the midrib occurred first in the basipetal part and then at the leaf tip where vessels are narrower. The distance from the midrib tip is a good predictor of the variation in vessel diameter along the 1st order veins in A. pseudoplatanus leaves and this anatomical pattern seems to have an effect on hydraulic integrity since wider vessels at the leaf base embolize first.

Allometric co‐variation of xylem and stomata across diverse woody seedlings

“…When considering the total water path length (e.g. by sampling the anatomical cross-section at the stem base), our results are in line with our prediction that there should be isometric scaling both between total leaf area and xylem conductance area and between total stomatal conductance area and xylem conductance area (Echeverría et al, 2019;Fiorin et al, 2016;Lechthaler et al, 2019;Meinzer & Grantz, 1990).…”

“…When considering the total water path length (e.g. by sampling the anatomical cross‐section at the stem base), our results are in line with our prediction that there should be isometric scaling both between total leaf area and xylem conductance area and between total stomatal conductance area and xylem conductance area (Echeverría et al, 2019; Fiorin et al, 2016; Lechthaler et al, 2019; Meinzer & Grantz, 1990). Further studies are needed to integrate the relations between leaf area, stomatal area and xylem conductance area from the perspective of the (three dimensional) water transport system from single‐leaf level to whole‐plant level.…”

“…The xylem system of vascular plants generally features a ‘tip‐to‐base’ widening with the maximal number of the narrowest conduits in the terminal parts; the size of these terminal conduits should not vary with plant size (or leaf size) (Lechthaler, Colangeli, Gazzabin, & Anfodillo, 2019; Rosell & Olson, 2019; West, Brown, & Enquist, 1999). With this hierarchical and basipetally widening xylem architecture, the energy cost of long‐distance water transport is minimized (Anfodillo, Carraro, Carrer, Fior, & Rossi, 2006; Shinozaki, Yoda, Hozumi, & Kira, 1964; West et al, 1999).…”

“…We ask: are there scaling relationships between total stomatal area and xylem cross‐sectional area across species, at the entire plant and at individual‐leaf level? Specifically, we zoom in on the terminal part of water exchange (from minor vessels to stomata), and ask: does the minor vessel number (which scales with leaf area; see Lechthaler et al, 2019; Rosell & Olson, 2019) scale with stomatal number per leaf and per plant across these woody seedlings? The conceptual picture should deepen our understanding of plants' water transport system and have broad implications for integrating xylem architecture and stomatal distribution.…”

From Carlquist’s ecological wood anatomy to Carlquist’s Law: why comparative anatomy is crucial for functional xylem biology

“…In terms of carbon, it would cost much less for conduits in the stem to coalesce tip-to-base into fewer and fewer wider and wider conduits, as animal circulatory systems do (McCulloh et al, 2003(McCulloh et al, , 2004(McCulloh et al, , 2009Gleason et al, 2018). And while there is marked coalescence in the leaves (Gleason et al, 2018;Lechthaler et al, 2019;Rosell and Olson, 2019), the most conspicuous observation regarding conductive systems in the stem is that they are made up of many parallel conduits (McCulloh et al, 2004(McCulloh et al, , 2009Bettiati et al, 2012). A plausible hypothesis is that multiple conduits provide robustness against the failure of some conduits to factors such as freezing or drought-induced embolism, fungal attack, or penetration by herbivores, an idea that was first introduced as far as I have been able to determine by Carlquist (Carlquist, 1977).…”