Photo-selective nets differentially affect microclimatic conditions, leaf physiological characteristics, and yield in hazelnut (Corylus avellana L.)

Photo-selective colored nets have been used as a tool to reduce climatic stress and improve yields in horticultural crops, but there is no knowledge regarding responses of hazelnut crops under these nets. The objective of this research was to study the influence of photo-selective nets on the microclimate, physiological characteristics of leaves, and yield in hazelnut. During three consecutive seasons, a hazelnut orchard ´Tonda di Giffoni´ was covered with black, blue-gray, and pearl-gray colored nets with a standard density of 4 warp and weft threads cm −1 . Uncovered trees were used as the control. Microclimatic conditions (solar radiation intensity and composition, air temperature, relative humidity, and vapor pressure deficit, VPD), yield components (accumulated yield; yield by harvest date; fruit weight, FW; and seed weight, SW), and leaf physiological characteristics (net photosynthesis rate, A n ; stomatal conductance, g s ; specific leaf weight, SLW; and stomatal density, SD) were evaluated. Pearl-gray netting had the greatest increase in diffuse (47%) and global (5%) solar radiation compared to blue-gray and black nettings. VPD decreased by 12% under black netting, but only by 5% under pearl-gray and blue-gray netting. Pearl-gray nets significantly increased accumulated yield, FW, and SW by 12, 13, and 6% compared to the control, respectively. Black and blue-gray nets reduced SD by 8 and 30% and SLW by 15 and 20%, respectively. Pearl-gray netting did not alter either SD or SLW. A significant relationship between A n and g s was found under all nets, but not for the control. The relationship between A n and g s was significantly positive for pearl-gray netting and negative for blue-gray netting. Photo-selective netting is a physiology-based tool that improves yield in hazelnut orchards under extreme climate conditions. Pearl-gray netting is the most promising alternative for this fruit crop.