How water supply during leaf development drives water stress response in Corylus avellana saplings

tCorylus avellana L. (hazelnut) is one of the world’s major nut crops, and is considered a sensitive species towater stress having a low capacity for stomatal regulation. Knowledge of hazelnut response to water stressis important from an economical point of view since water stress affects fruit quality and production. Inthis context, the effects of three different water regimes imposed during leaf development of hazelnutsaplings were analyzed. The results suggested that saplings which formed leaves under moderate andsevere-water stress regimes (MS and SS saplings, respectively) displayed several anatomical, morpho-logical and physiological acclimations compared to those developed under a well-watered regime (WWsaplings), 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) (by15% and 36%, mean value, respectively) compared to WW saplings. At a physiological level, stressed SSand MS saplings show higher dark respiration rates (RD), an improved photo-protection mechanism anda higher capacity to dissipate the excess of excitation energy (i.e. a higher carotenoid to chlorophyll ratio;a lower PSII) in respect to stressed WW saplings. During the imposed water stress, the 18% increase ofthe intrinsic water use efficiency (iWUE) in all three treatments attests to the stomatal control in thenet assimilation rate (AN) decrease. Taking into account that in the Mediterranean area supplementalirrigation in hazelnut orchards is required and that ground water supplies are declining while energycosts of irrigation are increasing, these results may provide important findings from an agricultural pointof view concerning irrigation decisions about the water supply to hazelnut saplings.