Woody tissues and vulnerability to xylem embolism in angiosperms

Plants frequently operate at leaf water potentials close to critical thresholds of conductivity loss by embolism formation. Therefore, it is expected that they evolved mechanisms either to limit embolism formation and spread, or to restore the hydraulic functionality. Species less vulnerable to embolism formation are commonly reported to have a higher wood density (WD). Nevertheless, the functional meaning of this relationship is still uncertain. We measured P50, WD, and the percentage of tissues composing wood (parenchyma cells, PATOT; vessel area, VA; fibre area, FA) on branches of angiosperm species. A dataset of published data on anatomical and hydraulic traits, including information on non-structural carbohydrates content (NSC), was also compiled. Less vulnerable species (i.e. more negative P50) had higher WD. This relationship was driven by either PATOT or FA, which were both significantly related to P50 and inversely related to each other. While remains uncertain why the amount of fibres relate to P50, the relationship between PATOT and P50 would support the hypothesis that parenchyma has a fundamental role in embolism recovery, thus providing a functional explanation to the relationship between WD and P50 in angiosperms.