| Sumario: | Avocado trees are native to humid tropical and sub-tropical regions. However, when they are cultivated in regions with a typical Mediterranean climate, especially during summer, are exposed to high temperatures, low relative humidity, and high solar radiation, which can seriously affect plant water status and several physiological processes of the crop. To minimize these stressful conditions, the use of shade nets is an agronomical technique that permits to create 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. This study has been carried out in a commercial orchard of young avocado trees cv. ‘Hass’ grafted on ‘Duke 7’ rootstock in Callosa d’En Sarrià (Alicante), Spain. Two crop systems were established in 2021, open-air and shading (by using a shade net). The physiological study consisted in determining daily variations of tree water status by measuring stem water potential (Ψstem), and simultaneously gas exchange (stomatal conductance, gs and leaf transpiration rate, Eleaf) and leaf chlorophyll fluorescence [quantum yield of PSII (ΦPSII) and electron transport rate (ETR)] by using an advanced leaf porometer (LI-600). 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, gs remained significantly more open after midday in shaded trees, allowing higher leaf transpiration and cooler leaf temperature (Tleaf). A similar daily pattern was followed by chlorophyll fluorescence parameters, ΦPSII and ETR, showing the lowest values at midday. In shaded plants, ΦPSII and ETR values remained higher after midday than in open-air plants, suggesting a lower photochemical inhibition of the photosynthesis by heat stress. In this sense, was found that ΦPSII and ETR were non-linear correlated with Tleaf, falling sharply when Tleaf overpassed 35 ºC. The effect of shading on the environmental factors had a lower impact on daily patterns of leaf gas exchange and leaf chlorophyll fluorescence parameters in autumn. Thus, the use of shade nets represents an agronomic alternative technique to open-air, for cultivation of avocado in Mediterranean climate conditions
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