Coordinated regulation of water relations and leaf succulence in beet (Beta vulgaris L.) under interacting salinity and soil moisture stress

Salinity and soil water limitation frequently co-occur in semi-arid environments, yet their combined effects on plant water regulation remain insufficiently understood. In this study, we examined how soil moisture influences the physiological responses of beet ( Beta vulgaris L.) to increasing salinity, focusing on water relations, osmotic adjustment, and leaf succulence. Beet ( B. vulgaris L.) plants were grown in a controlled soil system under a 5 × 3 factorial arrangement with four replicates, combining five irrigation water salinity levels (0–8 dS m⁻¹) and three soil moisture conditions (100%, 90%, and 80% of field capacity). Soil electrical conductivity and osmotic potential were monitored, and plant responses were assessed through biomass production, relative water content, leaf succulence, electrolyte leakage, plant water potential, and osmotic adjustment. Salinity increased osmotic adjustment and leaf succulence while progressively reducing relative water content and plant water potential. However, these responses depended on soil moisture level, indicating an interaction between osmotic and matric constraints. Moderate salinity (4 dS m⁻¹) combined with 90% field capacity promoted the highest biomass accumulation and was associated with enhanced osmotic adjustment and succulence. These findings indicate that osmotic adjustment and leaf succulence function as complementary mechanisms contributing to the maintenance of plant water status under interacting salinity and soil moisture stress.