Leaf Thickness and Electrical Capacitance As Measures of Plant Water Status.

Plant-based sensors can potentially be an answer to mitigate the shortcomings of the common plant water status monitoring methods. In this study, leaf thickness and leaf electrical capacitance (CAP) were investigated as indicators of water stress. The experiment was conducted on a tomato plant (Solanum lycopersicum) in a growth chamber with a constant temperature of 28 °C and 12-hour on/off photoperiod for 11 days. Soil volumetric water content, θ, was measured by a soil moisture sensor. The soil water content was maintained at field capacity for the first three days and allowed to dehydrate thereafter, over a period of eight days. The daily leaf thickness variations were minor with no significant day-to-day changes between soil moisture contents between field capacity and wilting point. Leaf thickness changes were more noticeable at soil moisture contents below the wilting point until leaf thickness stabilized during the final two days of the experiment when moisture content was 0.11. CAP was roughly constant throughout the experiment, at a minimum value during the dark periods and increasing rapidly during periods of light, implying that CAP was a reflection of photosynthetic activity. The daily CAP variations decreased when soil moisture was below the wilting point and completely ceased below a soil volumetric water content of 0.12, suggesting that the effect of water stress on CAP was observed through its impact on photosynthesis. The results suggested that leaf thickness and CAP can be used for estimating plant water status.