Development of a laser-induced fluorescence imaging system for root activity and rhizosphere visualisation

Non-invasive methods that enable continuous monitoring of spatial and temporal variations of physical and chemical parameters in the roots and the rhizosphere in situ are required in order to study the complex soil–roots interactions. In this work we present the use of laser-induced fluorescence imaging for visualizing these processes. The system consists of a Nd:YAG Q-switched laser that excites the root and rhizosphere auto-fluorescence, and an intensified gated camera (intensified charged coupled device (ICCD)) that is synchronized with the laser so that it captures the very short auto-fluorescence signal even in broad daylight. By using very short gating times (1 ns) and varying the delay between the laser pulse and the gating operation, time-resolved fluorescence profiles are obtained for each pixel in the image. The potential of the system is illustrated with several examples that show that both fluorescence intensity and temporal evolution profiles provide information about root activity and root–soil interactions.