Shade Nets Improve Gas Exchange and Chlorophyll Fluorescence in Young Avocado Trees Grown Under Mediterranean Conditions

Avocado trees (<i>Persea americana</i> Mill.) grown in Mediterranean conditions are exposed to high temperatures and intense solar radiation during summer, factors that can severely compromise plant water status and key physiological processes. To minimize these stressful conditions, the use of shade nets is an agronomical technique that permits the creation of an optimal microclimate for crop development. Thus, the aim was to evaluate the effects of shade netting on the physiological response of young avocado trees commercially grown under Mediterranean climatic conditions. The main results showed similar circadian rhythms of plant water status under both crop systems (open-air and shaded) in both seasons. However, the use of shading nets altered the circadian rhythm of leaf gas exchange. In summer, stomatal conductance (<i>g_s</i>) remained significantly more open after midday in shaded trees, allowing higher leaf transpiration (<i>E_leaf</i>) and cooler leaf temperature (T_leaf). A similar daily pattern was observed in chlorophyll a fluorescence parameters, including the effective quantum yield of photosystem II (ΦPSII) and the electron transport rate (ETR), with the lowest values occurring at midday. In shaded plants, ΦPSII and ETR remained higher after midday than in open-air, suggesting a lower photochemical inhibition of photosynthesis caused by heat stress and photoinhibition. Thus, the use of shade nets represents an agronomic alternative technique for cultivating avocados in Mediterranean climate conditions.