“…On the other hand, the hydraulic connectivity between the soil water reservoir and the plant water pathway relies on a negative water potential gradient created by leaves water transpiration. For comprehensively investigating the plant-water relation, various sensing techniques have been developed, such as those for leaf stomatal conductance (Friend et al, 1989;Steppe et al, 2006;Blonquist et al, 2009), leaf water potential (Turner and Long, 1980;Zimmermann et al, 2008), leaf temperature (Hashimoto et al, 1984;Rahkonen and Jokela, 2003;Gontia and Tiwari, 2008), leaf thickness (Li et al, 2009;Seelig et al, 2012), stem water potential (Choné et al, 2001;Yang et al, 2012), stem diameter variation (Fernández and Cuevas, 2010), stem sap flow rate (Č ermák et al, 1973;Bakfr and Van Bavel, 1987;Smith and Allen, 1996;Trcala and Č ermák, 2012), stem water content (Wullschleger et al, 1990;Irvine and Grace, 1997) and root water potential/pressure (Fiscus, 1972;De Swaef et al, 2013). However, even though these sensors provide different physiological information to support insights into plant water status, none provides a single measure that is well correlated with the numerous factors influencing plant water stress (Kramer, 1988).…”