Apple trees’ behavior to a single-season megadrought stress

Abstract

Extreme weather events such as megadroughts (long duration and intense droughts) are becoming common in regions with Mediterranean climates and threaten the continuity of fruit production. In this context, this study assesses the effects of a single-season megadrought on the physiological response and mortality of mature apple trees in a high-density orchard. Two treatments were imposed in two weighing lysimeters with four trees in each one, (i) Control: fully irrigated according to the crop evapotranspiration; and (ii) Drought: rainfed from 7 May 2023, until the end of the season. Trees’ evapotranspiration and trunk water potential were continuously monitored during the experiment in combination with periodic measurements of the soil water content, stomatal conductance, midday stem water potential, and apple size. The trunk water potential of apple trees in the drought lysimeter during the 2023 season fell below − 4.5 MPa, with stomatal conductance decreasing from 0.4 mmol m− 2 s− 1 before withholding irrigation to 0 mmol m− 2 s− 1 60 days later. In the following spring 2024, the four apple trees subjected to the megadrought were agronomically dead (did not sprout). Our results showed that, for apple trees, a threshold value of water potential of -3.5 MPa must not be surpassed to ensure the tree survival, while values below − 4.0 MPa for 27 days cause the death of the trees.