Plant hydraulics and measurement of vulnerability to embolism formation: a guide for beginners

Prolonged and/or intense drought leads to the deterioration of plant water balance, inducing embolism formation in the water conducting system, the xylem. The consequent loss of water transport capacity from roots to leaves (hydraulic failure) has been proposed as a main driver of plant mortality. Substantial inter- and intraspecific variation of resistance to embolism formation has been reported in plants. Hence, screening of different species/individuals is key to project the impact of future climate on ecosystems, while supporting breeding and reforestation. This review seeks to explain the mechanisms of water transport in plants and the phenomenon of embolism formation under drought stress by using concise and straightforward scholarly language. The main aim is to introduce non-expert readers (students, nonacademics, and academics from different scientific fields) to plant hydraulics and the controversial world of methods for measuring the vulnerability to embolism formation. To convey the message in full, we provide ranges of water potential values and widely used drought resistance indexes characterizing plants from different biomes. Various established methods used worldwide to monitor hydraulic efficiency under stress and measure hydraulic vulnerability by means of curves of different plant organs are introduced. Both classical widely used destructive methods and current non-destructive techniques, which have been gaining momentum in the last decade, are described. The main advantages and disadvantages of each method are briefly discussed to support decisions and selection of the most suitable method in experimental practice.