Multi-scale assessment of plant water status in Diospyros kaki grafted onto D. lotus and D. virginiana under water deficit

This study analyses drought response strategies in persimmon rootstocks by evaluating the physiological responses of persimmon ( Diospyros kaki Thunb.) cv. ‘Rojo Brillante’ trees grafted onto D. lotus and D. virginiana under summer water conditions in the SE of Spain. Fully irrigated trees (100% ET c ) were compared with trees subjected to irrigation restriction until midday stem water potential (Ψ stem ) reached −1.6 MPa (severe water deficit). Measurements of soil water content, trunk water potential (Ψ trunk ) and sap flow were monitored, together with temporal determinations of Ψ stem , midday leaf water potential and leaf gas exchange. In addition, UAV-based thermal and multispectral indicators were obtained at peak water stress. Our results revealed contrasting hydraulic strategies between rootstocks. D. lotus showed physiological traits consistent with a more anisohydric-like response, with rapid decreases in Ψ stem and Ψ trunk , whilst maintaining relatively stable leaf gas exchange. In contrast, D. virginiana exhibited a more conservative stomatal regulation, suggesting a more isohydric-like behaviour, under water deficit conditions. Among the plant-based indicators, Ψ trunk showed the highest sensitivity (S) and reliability for detecting drought stress. Sap flow measurements reflected transpiration dynamics, but with lower sensitivity, mainly due to differences in canopy size between rootstocks. UAV-derived spectral indices were primary driven by structural differences between rootstocks, whilst canopy temperature was the most sensitive remote sensing indicator to water deficit. These findings suggest that drought detectability in persimmon is strongly driven by rootstock-dependent hydraulic behaviour, highlighting Ψ trunk as a reliable plant-based indicator of persimmon water status under the conditions evaluated in this whole-tree transpiration study. Additionally, D. virginiana may represent a promising rootstock option under semi-arid Mediterranean conditions.