Effect of Microclimatic Conditions on Physiological Parameters of Hazelnuts

This study was conducted to determine the effects of microclimatic conditions, which directly and indirectly affect the yield and quality of hazelnuts, on physiological characteristics. The study was carried out on ‘Tombul’, ‘Palaz’ and ‘Kalınkara’ hazelnut varieties (Corylus avellana L.), which are important commercial varieties, in three complete hazelnut orchards with different microclimatic conditions in two vegetation periods in 2021 and 2022 in Yalıköy town of Fatsa district of Ordu province (Türkiye). The experiment was designed according to the randomized block trial design with 3 replications. The results of the research revealed that the changes in physiological parameters vary depending on the orchards and the varieties. As sun exposure increased in the ‘Tombul’ variety, the chlorophyll value and tissue relative water content decreased on July 25, and the number of stomata increased. The change in chlorophyll value and number of stomata on July 25 in the ‘Palaz’ variety was similar to the ‘Tombul’ variety. In ‘Kalınkara’ variety, unlike the other two varieties, the change in leaf temperature on July 10 according to orchards was significant and the change in the number of stomata was found to be similar to the other two varieties. On the other hand, the highest leaf temperatures in all three varieties were determined in 2021 and the highest chlorophyll values in 2020. Unlike ‘Palaz’ and ‘Kalınkara’, the tissue relative water content on August 3 in the ‘Tombul’ variety was determined to be higher in 2021. As a result, it can be said that important physiological parameters in hazelnuts may vary primarily depending on the variety, but also according to the sunshine duration of the orchards, years, and therefore, the microclimatic conditions of the orchards should also be taken into account in the evaluations regarding yield and quality.