Introducing terahertz technology into plant biology: A novel method to monitor changes in leaf water status

We present a novel, non-destructive method for determination of changes in leaf water content in the field based on terahertz (THz) technology. In this method, terahertz waves, which are strongly absorbed by water, are generated and detected using a photomixer that converts the optical beat signal of two interfering diode lasers into THz radiation. This allows a coherent detection as basis for the determination of changes in leaf water contents. The reliability of this innovative method was verified by monitoring changes in the leaf water content of young coffee plants in parallel using classical, destructive thermogravimetrical measurements as well as by THz spectroscopy. The broad applicability of this novel device was shown by long- and short-term measurements. The changes in leaf water content during drought stress induced dehydration as well as during the course of rapid re-hydration after re-watering vividly highlight the tremendous potential of this novel technique and its high reliability. The findings presented here provide the basis for THz-based in vivo determination of changes in the leaf water content under field conditions.