Short Scientific Visit: techniques to measure embolism in plants

Khaoula Ben Baaziz describes her short scientific visit,hosted by the French National Institute for Agricultural Research (INRA).

According to the tension-cohesion theory sap is transported under tension (negative pressure) in trees.. Since water is physically unstable under negative pressure, there is a risk of cavitation. Cavitation or embolism can be caused by drought and provoke the blockage of  water flow  due to the presence of air bubbles in the xylem pipes. Cavitation resistance is characterized by a vulnerability curve (VC) showing the relative changes in the amount of embolism as a function of xylem pressure. Many techniques are employed to induce xylem cavitation by water stress like bench drying, air pressurization and centrifugation. The techniques for measuring cavitation and embolism in plants are also very diverse.


xylem apparatus 250.jpg : 53.6748046875KbThe objective of my scientific visit was to be trained in techniques to measure embolism in plants.

These techniques can be dividedinto three groups: the acoustic detection of cavitation, observations of xylem water content and the hydraulic detection of embolism. According to the latter method, we measure xylem embolism via its effect on the loss of xylem conductance using the Xyl’em apparatus. This technique quantifies the degree of embolism in a xylem segment. In the case of embolism, stem hydraulic conductance will be reduced from Ki to Kmax. The percentage loss of conductance (PLC) is computed as PLC=100 x (1- Ki / Kmax). If PLC=0% none of the conduits were embolised and if PLC=100% then all the conduits are embolised.

pression chamber 250.jpg : 60.3310546875KbExperiments were conducted on Juglans regia and Populus tremula x alba branches. The latter techniqueis  applied in Quercus suber branches and other forest trees in our institute (Institut National de Recherches en Génie Rural, Eaux et Forêts (INRGREF),Tunisia) to study their vulnerability to cavitation. It was a very interesting experience allowing me to discover and operate with new techniques especially in a laboratory which has more than 25 years of experience in xylem embolism measurements.


I would like to thank Dr Hervé Cochard and Dr Têté Barigah for their precious explanations, also all members of the laboratory PIAF in INRA Clermont Ferrand, France for their warm welcome. I thank also the EFIMED for giving me a chance to make this visit.

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