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• Drought-induced xylem embolism is a serious threat to plant survival under future climate scenarios. Hence, accurate quantification of species-specific vulnerability to xylem embolism is a key to predict the impact of climate change on vegetation. Low-cost hydraulic measurements of embolism rate have been suggested to be prone to artefacts, thus requiring validation by direct visualization of the functional status of xylem conduits using nondestructive imaging techniques, such as X-ray microtomography (microCT). • We measured the percentage loss of conductance (PLC) of excised stems of Laurus nobilis (laurel) dehydrated to different xylem pressures, and compared results with direct observation of gas-filled vs water-filled conduits at a synchrotron-based microCT facility using a phase contrast imaging modality. • Theoretical PLC calculated on the basis of microCT observations in stems of laurel dehydrated to different xylem pressures overall were in agreement with hydraulic measurements, revealing that this species suffers a 50% loss of xylem hydraulic conductance at xylem pressures averaging--3.5 MPa. • Our data support the validity of estimates of xylem vulnerability to embolism based on classical hydraulic techniques. We discuss possible causes of discrepancies between data gathered in this study and those of recent independent reports on laurel hydraulics. [ABSTRACT FROM AUTHOR]

We investigated the hydraulic architecture of young olive trees either self-rooted or grafted on rootstocks with contrasting size-controlling potential. Clones of Olea europea L. (Olive) cv ‘Leccino’ inducing vigorous scion growth (Leccino ‘Minerva’, LM) or scion dwarfing (Leccino ‘Dwarf’, LD) were studied in different scion/rootstock combinations (LD, LM, LD/LD, LM/LM, LD/LM and LM/LD). Shoots growing on LD root systems developed about 50% less leaf surface area than shoots growing on LM root systems. Root systems accounted for 60–70% of plant hydraulic resistance (R), whereas hydraulic resistance of the graft union was negligible. Hydraulic conductance (K = 1/R) of LD root systems was up to 2.5 times less than that of LM root systems. Total leaf surface area (AL) was closely and positively related to root hydraulic conductance so that whole-plant hydraulic conductance scaled by AL did not differ between experimental groups. Accordingly, maximum transpiration rate and minimum leaf water potential did not differ significantly among experimental groups. We conclude that reduced root hydraulic conductance may explain rootstock-induced dwarfing in olive. [ABSTRACT FROM PUBLISHER]

We studied changes in the hydraulic conductance of leaves (Kleaf) between dawn and dusk during the growth period (July) and at midday at the beginning of autumn in four tree species. The main objectives of the study were to check the extent of diurnal and seasonal changes in Kleaf and the relationships between Kleaf, irradiance and leaf gas exchange. Two evergreen (Aleurites moluccana and Persea americana) and two deciduous trees (Platanus orientalis and Quercus rubra) were studied. Leaf hydraulic conductance was measured every 2 h between 0700 and 1900 h in July and compared with values measured between 0900 and 1300 h in October. Other variables measured were photosynthetically active radiation (PAR), leaf conductance to water vapor (gL) and water potential (ΨL). In July, Kleaf varied by up to 75% in Pe. americana on a diurnal basis and by at least 44% in Q. rubra. The diurnal time course of Kleaf showed a distinct increase between dawn and late morning (1100 h) and a subsequent decrease in the evening in A. moluccana and Pl. orientalis, whereas in the other two species, Kleaf was highest just after dawn and lowest in the evening. In October, Kleaf of all the species studied was lower than in July, with differences of 20 to 28% for A. moluccana and Pl. orientalis and of 66 to over 70% in Pe. americana and Q. rubra, respectively. Significant correlations were found between PAR and Kleaf (in all species) as well as between gL and Kleaf (in three out of four species). Leaf habit (evergreen or deciduous) did not influence absolute values of Kleaf or its diurnal variation. [ABSTRACT FROM AUTHOR]