Stem water potential, stomatal conductance and yield in irrigated apple trees

Abstract

Plant-based indicators of water status, such as midday stem water potential (Ψstem) and leaf stomatal conductance (gs), are used to optimise irrigation scheduling in horticultural crops because they integrate the effect of soil and climatic conditions and the internal physiological constraints. The use of these indicators relies on experimentally acquired thresholds that relate the value of the indicator to negative effects on yield. In five irrigation treatments, we monitored yield, fruit size and the courses of Ψstem and gs throughout four consecutive growing seasons. We found that Ψstem was more sensitive to irrigation treatment than gs. Both indicators increased with available soil water content (ASWC) and decreased with evaporative demands of the atmosphere (ETC). On a seasonal basis, crop load had a stronger impact on gs than Ψstem. In summary, our study explored the effect of environmental conditions and crop load on plant-based indicators of tree water status and can be useful for establishing thresholds for irrigation scheduling in apple tree orchards.