Demonstration of continuous non-invasive monitoring of plant metabolism using mid-infrared photoacoustic spectroscopy
Life is a rhythmic process driven by cellular and physiological mechanisms that allow plants to respond and adapt to their environment. In addition to natural fluctuations, plants are increasingly exposed to environmental stresses, mainly caused by climate change and anthropogenic pollution. Multiple approaches across different biological scales (gene, cell, metabolite, and physiology) have shed light on acclimation mechanisms but generally lack sufficient temporal resolution. Establishing a non-invasive and high-temporal-resolution monitoring method to measure plant activity across different conditions is therefore needed to fully assess how plant metabolism changes under stress. Here, we established a novel approach to perform continuous and non-invasive mid-infrared photoacoustic spectroscopy on vascular plants, with the aim of identifying and monitoring the chemical composition of peripheral tissues, including sap, over periods ranging from a few minutes to several months. We describe an experimental setup, the physics underlying its operation, and present a multi-day acquisition. Compared with controls, data enabled to identify a diurnal pattern, with peaks of approximately equal duration, that recurred consistently over the experiment. Estimations of the impact of instrumental and environmental fluctuations indicate that the signal amplitude and trends cannot be explained by instrumental drifts. The experiment thus demonstrated the detection of a signal associated with plant physiological activity. While its origins remain to be clarified, this preliminary experiment demonstrates the feasibility of the measurements and provides a basis for future developments.