Stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees

Abstract

Electrical plant signaling as a variation potential (VP) occurs in response to a wide range of stimuli, and it is associated with the induction of sudden changes in xylem pressure. Additionally, there is evidence that electrical potential (EP) of plants changes with changing soil water content. Therefore, the use of EP as a direct plant measurement of plant water status may have potential as water stress monitoring information. EP measurements within plant stems indirectly correlate with sap flow (SF), which is one possible variable for estimating plant water use. However, whether this relationship is stable under drought conditions is not known. The present work investigated the relationships between SF and EP variations during an 18-day drought period on three avocado trees to test the hypothesis that the relationships between SF and EP may be lost due to drought intensity. The results showed that short-term variations in EP were positively associated with vapor pressure deficit (VPD) and SF variations but negatively associated with soil water content (SWC). An increase in VP emissions was observed as drought advanced, which was negatively associated with stem water potential (SWP). After 18 days of drought, irrigation almost completely suppressed short-term variations in EP. The present work provides preliminary results that strongly suggest a relationship between drought stress and EP variations in plant stems. Further research is needed to confirm whether the EP trends observed during drought are due to cavitation events and emission of VP signals and/or linked to other physiological processes, e.g., pH changes in response to drought or embolism. Meanwhile, the present work indicates that short-term variations in EP (dEP) are strongly associated with the intensity of drought stress, thus stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees.