AUTHOR=Zambonini Dario , Savi Tadeja , Rosner Sabine , Petit Giai 

TITLE=Consistent decrease in conifer embolism resistance from the stem apex to base resulting from axial trends in tracheid and pit traits

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1414448

DOI=10.3389/fpls.2024.1414448

ISSN=1664-462X

ABSTRACT=<sec><title>Introduction</title><p>Drought-induced embolism formation in conifers is associated with several tracheid and pit traits, which vary in parallel from stem apex to base. We tested whether this axial anatomical variability is associated with a progressive variation in embolism vulnerability along the stem from apex to base.</p></sec><sec><title>Methods</title><p>We assessed the tracheid hydraulic diameter (<italic>Dh</italic>), mean pit membrane area (<italic>PMA</italic>) and the xylem pressure at 50% loss of conductivity (<italic>P50</italic>) on longitudinal stem segments extracted at different distances from the stem apex (<italic>DFA</italic>) in a <italic>Picea abies</italic> and an <italic>Abies alba</italic> tree.</p></sec><sec><title>Results</title><p>In both trees, <italic>Dh</italic> and <italic>PMA</italic> scaled with <italic>DFA</italic><sup>0.2</sup>. <italic>P50</italic> varied for more than 3 MPa from the treetop to the stem base, according to a scaling of -<italic>P50</italic> with <italic>DFA<sup>-0.2</sup></italic>. The largest <italic>Dh</italic>, <italic>PMA</italic> and <italic>P50</italic> variation occurred for <italic>DFA</italic>&lt;1.5 m. <italic>PMA</italic> and <italic>Dh</italic> scaled more than isometrically (exponent <italic>b</italic>=1.2). Pit traits vary proportionally with tracheid lumen diameter.</p></sec><sec><title>Discussion and conclusions</title><p>Apex-to-base trends in tracheid and pit traits, along with variations in P50, suggest a strong structure-function relationship that is influenced by <italic>DFA</italic>. Although the effect of <italic>DFA</italic> on <italic>P50</italic> has not been extensively explored previously, we propose that analyzing the relationship between <italic>P50</italic> and <italic>DFA</italic> could be crucial for a comprehensive assessment of embolism vulnerability at the individual level.</p></sec>