The physical origin of the intermittent drying of leaves

We evidenced the origin of this intermittent dynamics, by creating a biomimetic leaf containing the basic elements of real leaves. Crucially, vein networks contain pits, which are nanometric constrictions between sap-conducting cells; we mimicked such pits by inserting constrictions between larger microfluidic channels, embedded within a flexible and permeable material, like the leaves.

We have recovered an intermittent drying dynamics, characterised by an arrest of the embolism inside the constriction, followed by a fast jump at the constriction exit. We have shown that two phenomena drive this dynamics: the pinning of an air/liquid interface on the corners of the constriction, and the channel compliance under the decrease of water pressure during the pinning phase. Therefore, in plants, pits act as capillary traps for embolisms... but only for a limited amount of time.

Reference
Keiser, L., Marmottant, P., & Dollet, B. (2022). Intermittent air invasion in pervaporating compliant microchannels. Journal of Fluid Mechanics, 948, A52.