Auteur(s)

Matthias Klepsch^1,*,†, Ya Zhang^1,*, Martyna M. Kotowska^2,3, Laurent J. Lamarque^4,5, Markus Nolf⁶, Bernhard Schuldt³, José M. Torres-Ruiz^4,7, De-Wen Qin⁸, Brendan Choat⁶, Sylvain Delzon⁴, Christine Scoffoni⁹, Kun-Fang Cao⁸, Steven Jansen¹

Résumé

According to the hydraulic vulnerability segmentation hypothesis, leaves are more vulnerable to decline of hydraulic conductivity than branches, but whether stem xylem is more embolism resistant than leaves remains unclear. Droughtinduced embolism resistance of leaf xylem was investigated based on X-ray microcomputed tomography (microCT) for Betula pendula, Laurus nobilis, and Liriodendron tulipifera, excluding outside-xylem, and compared with hydraulic vulnerability curves for branch xylem. Moreover, bordered pit characters  related to embolism resistance were investigated for both organs. Theoretical P50 values (i.e. the xylem pressure corresponding to 50% loss of hydraulic conductance) of leaves were generally within the same range as hydraulic P50 values of branches. P50 values of leaves were similar to branches for L. tulipifera (−2.01 versus −2.10 MPa, respectively), more  negative for B. pendula (−2.87 versus −1.80 MPa), and less negative for L. nobilis (−6.4 versus −9.2 MPa). Despite more narrow conduits in leaves than branches, mean interconduit pit membrane thickness was similar in both organs, but significantly higher in leaves of B. pendula than in branches. This case study indicates that xylem shows a largely similar embolism resistance across leaves and branches, although differences both within and across organs may occur, suggesting interspecific variation with regard to the hydraulic vulnerability  segmentation hypothesis.

Mots clés

Bordered pit, branch, embolism, hydraulic segmentation, leaf, microCT, pit membrane, xylem.