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Plants and variations of relative humidity : Bubbles nucleation in trees & Locomotion of Equisetum spores

Alexandre Ponomarenko

à 11h en salle C. Brot

I will present two responses of plants to the variations of relative humidity in surrounding air :

One is the response of a tree to a drought. It is known that under drought conditions (when air and soil both dry) the pressure in ascending sap decreases. This pressure reaches negative pressures where the sap becomes metastable and forms bubbles. Those bubbles form an embolism in the hydraulic pathway of trees, possibly causing their death. At the same time, during drought, sounds are heard in trees. I will present a device that enable to observe optically and acoustically a tree sample in conditions of drought.

The second is the locomotion of Equisetum spores caused by oscillations of air relative humidity : between dry and wet. The spores of this plant have a spherical body of 50µm size and four ’arms’ called elaters that have a hygroscopic response : they open and close with air humidity variations. We will see how this hygroscopic response participates to the locomotion of Equisetum spores.

Legend to the pictures :

- a bubble growing in a sap channel of pine tree

- a spore of Equisetum in air successively wet and dry

(UMR PIAF, INRA, Clermont-Ferrand, before LiPhy, Grenoble