Drought is an abiotic stress that may be aggravated by climate changes with increasingly warmer and drier summers. This is a severe problem in the chestnut crop in Portugal due to its need for water during this time, which is essential for good formation and development of the fruit. Si fertilization is referenced by several authors as important in the tolerance of plants under drought. The experiments were carried out in the field trial and chestnuts were fertilized with 0, 5, 7.5, and 10 mM

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... tassium silicate (SiK), which was applied to the soil and to the leaves and exposed to a non-irrigation and an irrigation phase during the summer. Results indicate that Si fertilization increased the relative water content and water potential, while the transpiration rate, stomatal conductance, and stomatal density were reduced under deficit irrigation in Si-treated plants (10 mM SiK). Moreover, the Si induces a higher photosynthetic activity and vessel frequency with a smaller diameter, promoting a higher relative hydraulic conductivity and a lower vulnerability to cavitation. This work suggests that Si can be used as a potential source to induce drought tolerance in chestnuts. photosynthetic rate; RC -relative hydraulic conductivity; RWC -relative water content; SD -stomatal density; Si -silicon; SiK -potassium silicate; VA -vessel area; VD -vessel diameter; VF -vessel frequency; WUE -water-use efficiency (= PN/E); Ψw -water potential. Acknowledgements: The authors would like to acknowledge Mrs. Cesaltina Machado, Mrs. Donzilia Costa, and Mrs. Helena Ferreira for their help with the assay installation. We thank Mr. Armindo Teixeira for his invaluable suggestions concerning the elaboration of xylem histological sections. We also thank for the support provided by the National Funds by FCT -Portuguese Foundation for Science and Technology, under the project UID/AGR/04033/2019.