An inconvenient truth about xylem resistance to embolism in the model species for refilling Laurus nobilis L.

Auteur(s)

Laurent J. Lamarque^1,2, Déborah Corso², José M. Torres-Ruiz², Eric Badel³, Timothy J. Brodribb⁴, Régis Burlett², Guillaume Charrier^2,5, Brendan Choat⁶, Hervé Cochard³, Gregory A. Gambetta⁵, Steven Jansen⁷, Andrew King⁸, Nicolas Lenoir⁹, Nicolas Martin-StPaul¹⁰, Kathy Steppe¹¹, Jan Van den Bulcke¹², Ya Zhang⁷, Sylvain Delzon²

Résumé

& Key message Direct, non-invasive X-ray microtomography and optical technique observations applied in stems and leaves of intact seedlings revealed that laurel is highly resistant to drought-induced xylem embolism. Contrary to what has been brought forward, daily cycles of embolism formation and refilling are unlikely to occur in this species and to explain how it copes with drought. & Context There has been considerable controversy regarding xylem embolism resistance for long-vesselled angiosperm species and particularly for the model species for refilling (Laurus nobilis L.). & Aims The purpose of this study was to resolve the hydraulic properties of this species by documenting vulnerability curves of different organs in intact plants. & Methods Here, we applied a direct, non-invasive method to visualize xylem embolism in stems and leaves of intact laurel seedlings up to 2-m tall using X-ray microtomography (microCT) observations and the optical vulnerability technique. These approaches were coupled with complementary centrifugation measurements performed on 1-m long branches sampled from adult trees and compared with additional microCT analyses carried out on 80-cm cut branches. & Results Direct observations of embolism spread during desiccation of intact laurels revealed that 50% loss of xylem conductivity (Ψ50) was reached at − 7.9 ± 0.5 and − 8.4 ± 0.3 MPa in stems and leaves, respectively, while the minimum xylem water potentials measured in the fieldwere − 4.2MPa during a moderate drought season. Those findings reveal that embolism formation is not routine in Laurus nobilis contrary to what has been previously reported. These Ψ50 values were close to those based on the flow-centrifuge technique (− 9.2 ± 0.2 MPa), but at odds with microCT observations of cut branches (− 4.0 ± 0.5 MPa). & Conclusion In summary, independent methods converge toward the same conclusion that laurel is highly resistant to xylem embolism regardless its development stage. Under typical growth conditions without extreme drought events, this species maintains positive hydraulic safety margin, while daily cycles of embolism formation and refilling are unlikely to occur in this species.

Mots clés

Xylemembolism, Drought resistance, Laurel, Refilling, Hydraulics, Desiccation