Seasonal effects of deficit irrigation on leaf photosynthetic traits of fruiting and non-fruiting shoots in almond trees

Abstract

We investigated seasonal trends in, and relationships between, leaf structural properties, leaf nitrogen concentration, and maximum (A(m)) and potential (A(p)) leaf net CO(2) 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 (W(a)), area and dry-mass-based leaf N concentrations (N(a) and N(w), respectively), and area and dry-mass-based A(m) (A(ma) and A(mw), 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, A(m) and A(p) were correlated negatively with W(a) and positively with N(w) for both the leaf classes and the irrigation regimes. When calculated with respect to total leaf N concentration, maximum photosynthetic nitrogen-use efficiency (PNUE(m)) was significantly higher in f-leaves than in nf-leaves, with no significant differences between the leaf classes among the irrigation regimes. However, when PNUE(m) 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 CO(2) 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.