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To determine whether partial rootzone drying (PRD) optimised leaf gas exchange and soil–plant water relations in almond (Prunus dulcis(Mill.) D.A. Webb) compared with regulated deficit irrigation (RDI), a 2 year trial was conducted on field-grown trees in a semiarid climate. Five irrigation treatments were established: full irrigation (FI) where the trees were irrigated at 100% of the standard crop evapotranspiration (ETc); three PRD treatments (PRD70, PRD50and PRD30) that applied 70, 50 and 30% ETc, respectively; and a commercially practiced RDI treatment that applied 50% ETcduring the kernel-filling stage and 100% ETcduring the remainder of the growth season. Measurements of volumetric soil moisture content in the soil profile (0–100cm), predawn leaf water potential (Ψpd), midday stem water potential (Ψms), midday leaf gas exchange and trunk diameter fluctuations (TDF) were made during two growing seasons. The diurnal patterns of leaf gas exchange and stem water potential (Ψs) were appraised during the kernel-filling stage in all irrigation regimes. When tree water relations were assessed at solar noon, PRD did not show differences in either leaf gas exchange or tree water status compared with RDI. At similar average soil moisture status (adjudged by similar Ψpd), PRD50trees had higher water status than RDI trees in the afternoon, as confirmed by Ψsand TDF. Although irrigation placement showed no effects on diurnal stomatal regulation, diurnal leaf net photosynthesis (Al) was substantially less limited in PRD50than in RDI trees, indicating that PRD improved leaf-level water use efficiency. [ABSTRACT FROM AUTHOR]

We investigated seasonal trends in, and relationships between, leaf structural properties, leaf nitrogen concentration, and maximum (Am) and potential (Ap) leaf net CO2 assimilation of 1-year-old fruiting (f) and current-year non-fruiting (nf) shoots in 5-year-old almond trees (Prunus dulcis (Mill.) D.A. Webb cv Marta). These trees had been subjected in the previous 4 years to either full irrigation (FI regime) or sustained deficit irrigation (DI) at 50% of standard crop evapotranspiration during the entire growing season (DI regime) in the semiarid climate of southeast Spain. Measurements were made during an entire growing season on sun-exposed leaves. Leaf dry mass per unit area (Wa), area and dry-mass-based leaf N concentrations (Na and Nw, respectively), and area and dry-mass-based Am (Ama and Amw, respectively) were lower in f-leaves than in nf-leaves. Changes in leaf structural attributes induced by DI were more pronounced in nf-leaves than in f-leaves, the latter being little affected. Over the entire growth season, Am and Ap were correlated negatively with Wa and positively with Nw for both the leaf classes and the irrigation regimes. When calculated with respect to total leaf N concentration, maximum photosynthetic nitrogen-use efficiency (PNUEm) was significantly higher in f-leaves than in nf-leaves, with no significant differences between the leaf classes among the irrigation regimes. However, when PNUEm was calculated with respect to photosynthetic N, no significant effect of leaf class or irrigation regime was observed. Overall, our results showed that DI and FI trees exhibited similar seasonal patterns of leaf structural properties and maximum and potential leaf net CO2 assimilation rates, but there were distinct N-allocation patterns between f- and nf-leaves. In the DI treatment, leaf structural adjustments appeared to operate to maintain a high N status in the leaves of fruit-bearing shoots, to the detriment of N resources allocated to vegetative shoots. [ABSTRACT FROM AUTHOR]