Journal Article

Hydraulic efficiency and safety of vascular and non-vascular components in <i>Pinus pinaster</i> leaves

Katline Charra-Vaskou, Eric Badel, Régis Burlett, Hervé Cochard, Sylvain Delzon and Stefan Mayr

Edited by Roberto Tognetti

in Tree Physiology

Volume 32, issue 9, pages 1161-1170
Published in print September 2012 | ISSN: 0829-318X
Published online August 2012 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tps071
Hydraulic efficiency and safety of vascular and non-vascular components in Pinus pinaster leaves

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Leaves, the distal section of the soil–plant–atmosphere continuum, exhibit the lowest water potentials in a plant. In contrast to angiosperm leaves, knowledge of the hydraulic architecture of conifer needles is scant. We investigated the hydraulic efficiency and safety of Pinus pinaster needles, comparing different techniques. The xylem hydraulic conductivity (ks) and embolism vulnerability (P50) of both needle and stem were measured using the cavitron technique. The conductance and vulnerability of whole needles were measured via rehydration kinetics, and Cryo-SEM and 3D X-ray microtomographic observations were used as reference tools to validate physical measurements. The needle xylem of P. pinaster had lower hydraulic efficiency (ks = 2.0 × 10−4 m2 MPa−1 s−1) and safety (P50 = − 1.5 MPa) than stem xylem (ks = 7.7 × 10−4 m2 MPa−1 s−1; P50 = − 3.6 to − 3.2 MPa). P50 of whole needles (both extra-vascular and vascular pathways) was − 0.5 MPa, suggesting that non-vascular tissues were more vulnerable than the xylem. During dehydration to − 3.5 MPa, collapse and embolism in xylem tracheids, and gap formation in surrounding tissues were observed. However, a discrepancy in hydraulic and acoustic results appeared compared with visualizations, arguing for greater caution with these techniques when applied to needles. Our results indicate that the most distal parts of the water transport pathway are limiting for hydraulics of P. pinaster. Needle tissues exhibit a low hydraulic efficiency and low hydraulic safety, but may also act to buffer short-term water deficits, thus preventing xylem embolism.

Keywords: Cavitation; collapse; conductivity; conifer; extra-vascular pathway; microtomography; needle; vulnerability; xylem; 3D visualization

Journal Article.  6662 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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