A new technique for monitoring plant transpiration under field conditions using leaf optical dendrometry

Monitoring plant transpiration (Ec) is important for quantifying irrigation amounts and maintaining optimum soil moisture conditions for maximum growth potential. However, real-time quantification of Ec dynamics under field conditions is still challenging due to technical limitations. Here, we present a new approach for monitoring plant water use using continuous measurement of stem water potential dynamics (psi stem) under non-limiting water conditions. According to Darcy's law, if daytime root to stem hydraulic conductance (Kr-s) remains constant and the contribution of plant capacitance to Ec is minimal or accounted for, then daytime Ec could potentially be continuously inferred from psi stem dynamics. We investigated the viability of this approach by first quantifying the dynamics of daytime Kr-s and the transient buffering effects of plant capacitance in irrigated plants of two crop species with contrasting physiology and life history: the perennial herbaceous Tanacetum cinerariifolium and the annual monocot Triticum aestivum. Daytime Kr-s dynamics and the effects of plant capacitance were determined by continuously and simultaneously measuring psi stem with optical dendrometers and Ec with gravimetric method under naturally variable conditions of light, temperature and humidity. Kr-s remained relatively stable throughout the day and the effects of plant capacitance were negligible in both species under field conditions implying that the dynamics of Ec can be inferred from psi stem. This was clearly supported by the close agreement between measured Ec and that predicted from the optically derived psi stem. We conclude that optical dendrometry has the potential to continuously monitor both Ec and plant hydration status at high ac-curacy and temporal resolution under naturally variable atmospheric conditions and optimum water supply. Combining these two aspects of the optically derived psi stem should create new opportunities to monitor crop water use and maintain plant hydration at optimum levels for maximum productivity in various crops under field conditions.

Automated summary

Monitoring plant transpiration is crucial for optimizing irrigation and soil moisture conditions. A new method using continuous measurement of stem water potential dynamics was proposed to monitor plant water use. The study found that daytime root to stem hydraulic conductance remained stable and the effects of plant capacitance were negligible, indicating that plant transpiration dynamics can be inferred from stem water potential. Optical dendrometers showed potential in continuously monitoring transpiration and plant hydration status with high accuracy and temporal resolution under varying atmospheric conditions and optimum water supply. This method could be beneficial for improving crop productivity by maintaining optimal plant hydration levels.