Intra-specific variability of stomatal sensitivity to vapour pressure deficit in Corylus avellana L.: a candidate factor influencing different adaptability to different climates?

Stomatal conductance is regulated by many factors such as air vapour pressure deficit (D), which can be the pivotal one affecting leaf gas exchange in species particularly sensitive to D such as C. avellana. The aim of this work was to evaluate stomatal sensibility to D and to determine correlations with hydraulics characteristics of leaves in three genotypes of C. avellana selected over centuries under different climatic conditions in the Italian peninsula. Among the three varieties Tonda Gentile delle Langhe (TGL), which was the one coming from northern Italy suffered the largest stomatal limitation at increasing levels of D in comparison with the other two cultivars [Tonda Romana (TR) and Tonda di Giffoni (TG), selected in central and southern Italy, respectively]. In all genotypes, photosynthesis decreased at high D although the reduction was mostly due to the rising of the temperature as suggested by the high values of sub-stomatal concentration of CO2. Concerning the hydraulic characteristics of the leaves, TG had considerable higher bulk elasticity compared with other two cultivars. These results contribute to explain the higher adaptability to different environments of TG and TR compared with TGL. Either the lower sensitivity to D of TG and TR and higher schlerophylly of TG might allow these cultivars to suffer less gas exchange limitations in hot and dry environments usually conducive to high D. Genotypic sensitivity to D represent one of the key factors to be considered in phenotyping protocols for sensitive species such as hazelnut.