A new approach to ascertain the sensitivity to water stress of different plant water indicators in extra-early nectarine trees

The sensitivity to water stress of different plant water indicators was evaluated during the late postharvest period of extra-early nectarine trees growing in a commercial orchard and submitted to two irrigation treatments: (i) a control (TC), irrigated at 120% of crop evapotranspiration to avoid any soil water limitations, and (ii) a water deficit treatment (TD), irrigated at 50% of TC. The plant indicators studied were: the maximum daily trunk shrinkage (MDS); trunk growth rate (TGR); midday stem water potential (Ψstem); leaf conductance (Gs); and net photosynthesis (Pn). Although the highest signal intensity (SI) values – the ratio of deficit irrigation treatment values to control values – were reached by TGR, Gs and Pn (2.6, 3 and 2.9, respectively), the sensitivity (S) values – calculated as the ratio of SI to coefficient of variation (SI CV−1) – were higher in Ψstem and MDS (14 and 11.4, respectively), since their CV values were the lowest (11 and 14%, respectively). A new approach (S*) is proposed to calculate the sensitivity of the plant water indicators, since the standard method can result in high sensitivity values without identifying differences between irrigation treatments. While S is more influenced by the CV values, S* would be influenced by both the SI and CV values.