Genotypic and intra-canopy variability of leaf sensitivity to vapor pressure deficit in Corylus avellana L

Vapor pressure deficit (VPD) is the driving force of leaf transpiration and it is positively related to air temperature and negatively related to relative humidity. Hazelnut is considered a species able to withstand limited increase of VPD. High VPD during the summer can induce significant stomatal limitations with significant short-term effects on leaf photosynthesis and long-term damage to the leaf apparatus. We investigated the leaf sensitivity to VPD in three C. avellana cultivars, ‘Tonda Gentile delle Langhe’ (TGL), ‘Tonda Romana’ and ‘Tonda di Giffoni’, and on leaves borne on long shoots, non-fruiting short shoots and fruiting short shoots of ‘Tonda di Giffoni’. TGL was the most sensitive to VPD and leaf temperature. Leaves on short shoots were more sensitive to VPD than leaves on long shoots. Leaves on fruiting short shoots had lower leaf gas exchange rates than those on non-fruiting short shoots and long shoots, respectively. Part of this variability was related to higher leaf mass per area of leaves borne on short shoots and to different osmotic potential. Leaf sensitivity to VPD can be an important physiological parameter influencing the adaptability of cultivars to scenarios of climate change and limiting the capability of leaves located on short shoots where nuts are borne to export carbohydrates.