Quantitative response and underlying mechanisms of tomato yield to irrigation lower limit and soil salinity

Lowering the irrigation lower limit is a potential strategy for improving crop water productivity in saline soils, but its effectiveness depends on soil salinity and physiological recovery after rewatering. This study investigated the yield response and underlying mechanisms of processing tomato under different irrigation lower limits and soil salinity levels during two growing seasons. Tomatoes were grown in sandy loam soil under plastic-mulched drip irrigation, with three initial soil salinity levels of 4.07, 11.17, and 18.26 dS m⁻¹ , expressed as the electrical conductivity of the saturated soil extract (ECe), and with four irrigation lower limits set as 75%, 65%, 55%, and 45% field capacity (θ FC ). Soil salinity and irrigation lower limit jointly regulated leaf ion accumulation, water status, abscisic acid (ABA) content, gas exchange, photosynthetic enzyme activity, dry matter accumulation, yield, leaf-level water use efficiency and irrigation water productivity. When the initial ECe was 11.17 dS m⁻¹ , soil salinity promoted osmotic adjustment, maintained leaf water status, stomatal conductance, chlorophyll, Rubisco activity, and F₁F₀-Adenosine Triphosphate (F₁F₀-ATP) synthase activity, thereby supporting photosynthetic recovery after rewatering. In contrast, when the initial ECe was 18.26 dS m⁻¹ , soil salinity increased Na⁺ accumulation, reduced K⁺ content, intensified ionic imbalance, and limited photosynthetic recovery. Yield and irrigation water productivity showed unimodal responses to the irrigation lower limit, indicating salinity-dependent optimal irrigation lower limits. Under the experimental conditions, the recommended irrigation lower limits were 65%, 60%, and 65% θ FC for soils with initial ECe values of 4.07, 11.17, and 18.26 dS m⁻¹ , respectively. These findings provide a physiological basis for developing soil salinity-specific deficit irrigation strategies.