The perennial scarcity of water resources in South-Eastern Spain drastically limits crop production. An alternative irrigation practice to conventional deficit irrigation is partial root-zone drying (PRD), which deliberately aims to impose soil moisture heterogeneity by independently watering different parts of the root zone to restrict crop water use.

Partial Root-Zone Drying and Crop Water Use Efficiency

While the agronomic benefits of PRD have usually been attributed to changes in chemical root-to-shoot signalling, recent results of our group have found that crop water use efficiency of lemon was improved without any change in ABA signalling, suggesting that alternative mechanisms may be important.

Potassium and Ethylene in PRD

Potassium plays a crucial role in cellular osmoregulation, contributing to osmotic water uptake and growth, but there has been little or no consideration of PRD effects on potassium status. K+ starvation favours ethylene synthesis which can inhibit the action of ABA on stomata, delaying their closure.

Soil Drying and Ethylene Dynamics

Soil drying stimulates the accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC, precursor of ethylene) in the root system, which after re-watering is transported from root to shoot and oxidized to ethylene in the leaves. Ethylene is involved in regulating multiple physiological processes including fruit ripening, leaf and flower abscission, and root and shoot growth inhibition.

Ethylene Production and Sensitivity

Ethylene production and sensitivity also modify stomatal conductance and photosynthesis. This research aims to explore alternative mechanisms by which alternated PRD (A-PRD) could affect crop K+ status and ethylene dynamics, thereby affecting physiological processes related to crop water use efficiency.

Experimental Design

To achieve this global objective, several experiments will be carried out in tomato or citrus plants grown in split-pots in a environment-controlled greenhouse. Plants will be grown in a low nutrient soil with different levels of potassium and will be subjected to two levels of watering (100% and 70% of crop evapotranspiration) and two types of irrigation (conventional deficit irrigation and A-PRD). Throughout each experiment, volumetric soil water content, leaf water potential, stomatal conductance, photosynthesis, xylem ABA and ACC concentrations, foliar ethylene production and crop and soil potassium concentrations will be studied.

Focusing on Crop Ethylene Dynamics

Focusing on crop ethylene dynamics and its relationship to specific physiological processes will improve our ability to optimise PRD application to improve crop water use efficiency.