Real-Time Observations of Leaf Vitality Extinction by Dynamic Speckle Imaging

Sap flow within a leaf is a critical indicator of plant vitality and health. This paper introduces an easy-to-use, non-invasive and real-time imaging method for sap microcirculation imaging. From the coherent backscattering of light on a leaf, we show that the acquisition frequency of dynamic speckle can be linked to the microcirculation speed inside the leaf. Thus, by accessing different ranges of sap flow velocities, we reveal in a non invasive way, the anatomy of the leaf's circulatory network with unprecedented richness. We experimentally validate the ability of the method to characterize in real time the vitality of a fig leaf by observing the continuous decrease of sap circulation, first in the smaller vessels and then in the larger ones, following the cutting of the leaf over a 48-hour period.