Leaf water relation parameters in almond compared to hazelnut trees during a deficit irrigation period

The influence of deficit irrigation on predawn leaf water potential (psi(pd)) and leaf gas-exchange parameters was analyzed in almond [Prunus dulcis (Mill.) D.A. Webb] and compared to hazelnut (Corylus avellana L.). Both species were planted in adjacent plots in which four irrigation treatments were applied: T-100%, T-130%, and T-70%, which were irrigated at full crop evapotranspiration (ETc), 1.3 x ETc, and 0.7 x ETc, respectively, and a regulated deficit irrigation (RDI) treatment, which consisted of full irrigation for the full season, except from middle June to late August when 0.2 x ETc was applied. Under nonstressful conditions, hazelnut had a lower net CO2 assimilation rate (A) (12.2 mu mol . m(-2). s(-1)) than almond (15.5 mu mol . m(-2). s(-1)). Reductions in net CO2 assimilation rate (A) induced by decreases in psi(pd) were higher in hazelnut than in almond. Gas-exchange activity from early morning to midday decreased in hazelnut for all irrigation treatments, but in almond increased in the well-watered treatments and decreased slightly or remained constant in the RDI. Hazelnut had a higher A sensitivity to variations in stomatal conductance (g(s)) than almond, especially at low g(s) values. The psi(pd) values in almond and hazelnut of the T-100% and T-130% treatments were affected by decreasing values in midsummer, but in hazelnut psi(pd) was probably also affected by sink kernel filling. These bets indicate that hazelnut RDI management could be more problematic than in almond.