Propagation of embolisms in tree leaves

This work is part of the PhySap project, born of a collaboration between InPhyNi (Nice), LiPhy (Grenoble) and PIAF (Clermont-Ferrand).

Why does sap ascend inside trees? To replace water lost through the leaves. Evapotranspiration enables plants to draw from the soil the water and the nutrients they need to thrive. In drought times, water contained inside xylem – the porous tissue in which sap ascends – may experience tension enough to undergo cavitation. Bubbles – embolisms – appear in the vessels and prevent the good passage of sap. Should drought last too long, tissues downstream from the embolisms would wither and the plant may eventually die. It is therefore important to study the appearance of embolisms in species of interest in order to predict their resistance to drought. My work consists in observing the spreading of such embolisms within tree leaves. Since the leaf is embolized in fits and starts, the goal is to characterize the dynamics of each burst, at very short time scales (tenths of milliseconds). Of course, it is expected that such dynamics differ between species, vein size, etc.