Trade-off between hydraulic sensitivity, root hydraulic conductivity and water use efficiency in grafted Prunus under water deficit

Sweet cherry is mainly cultivated in arid and semi-arid areas. In the last decade, these areas have experienced a dramatic reduction in rainfall, which has resulted in water shortage for sweet cherry. The use of specific rootstock and scion combinations could help improve the tolerance of plants to water shortage events. This study reports on the influence of rootstocks on whole-plant performance under water deficit as detected by hydraulic sensitivity, root hydraulic conductivity (Lp), water use efficiency and sugar content. Four Prunus rootstocks/scion combinations - 'Bing/Colt', 'Lapins/Colt', 'Bing/Mx60', 'Lapins/Mx60', and two self-rooted rootstocks Colt and Maxma 60 - were acclimated for 30 days and then exposed to well-watered (WW) and water deficit (WD) conditions for 36 days. Whole-plant transpiration and growth were both influenced by WD, and two groups were identified based on responses: 'Bing/Colt', 'Bing/Mx60' and 'Mx60' had an early reduction (conservative strategy), whereas 'Lapins/Mx60', 'Lapins/Colt' and 'Colt' had late reduction (productive strategy) in transpiration as WD increased. Among the combinations, 'Lapins/Colt' and 'Colt' showed a remarkable growth response to the WD being less affected in shoot and root biomass. The 'Colt' rootstock maintained a higher Ψgs50 (near-isohydric behavior) than combinations using the 'Mx60' rootstock (near anisohydric behavior). The relationship between Lp and the variation of Ψpre-dawn-Ψmidday showed differences among rootstock/scion combinations, and under WD condition the reduction in Lp induced by WD affected the whole-plant WUE of combinations differently. Sucrose and sorbitol content in leaves and roots of WD-tolerant combinations such as 'Colt' and 'Lapins/Colt', showed a remarkable increase under WD condition. Our finding highlights the importance of the specific interaction between rootstock and scion, suggesting that combinations characterized by a higher water uptake capacity under conditions of lower water availability would be sustainable under minimal to moderate water deficit.