LAUSR

Abstract Corylus avellana L. (hazelnut) is one of the world’s major nut crops, and is considered a sensitive species to water stress having a low capacity for stomatal regulation. Knowledge of hazelnut response to water stress is important from an economical point of view since water stress affects fruit quality and production. In this context, the effects of three different water regimes imposed during leaf development of hazelnut saplings were analyzed. The results suggested that saplings which formed leaves under moderate and severe-water stress regimes (MS and SS saplings, respectively) displayed several anatomical, morphological and physiological acclimations compared to those developed under a well-watered regime (WW saplings), giving them a greater capacity to cope with water stress. For instance, at a morphological level, MS and SS saplings had a higher leaf mass per unit of leaf area (LMA) and leaf tissue density (LTD) (by 15% and 36%, mean value, respectively) compared to WW saplings. At a physiological level, stressed SS and MS saplings show higher dark respiration rates (RD), an improved photo-protection mechanism and a higher capacity to dissipate the excess of excitation energy (i.e. a higher carotenoid to chlorophyll ratio; a lower ΦPSII) in respect to stressed WW saplings. During the imposed water stress, the 18% increase of the intrinsic water use efficiency (iWUE) in all three treatments attests to the stomatal control in the net assimilation rate (AN) decrease. Taking into account that in the Mediterranean area supplemental irrigation in hazelnut orchards is required and that ground water supplies are declining while energy costs of irrigation are increasing, these results may provide important findings from an agricultural point of view concerning irrigation decisions about the water supply to hazelnut saplings.