The Role of Calcium in Salinity Stress Alleviation: Mechanisms and Implications

Soil salinity is one of the most severe abiotic stresses limiting agricultural productivity worldwide by adversely affecting plant growth, development, and yield. Excessive salt accumulation disrupts ion homeostasis, induces osmotic and oxidative stress, impairs photosynthesis, and alters essential metabolic processes. Calcium (Ca²⁺) plays a pivotal role in enhancing plant tolerance to salinity by functioning as both a structural component and a critical secondary messenger in stress signaling pathways. This review comprehensively examines the mechanisms through which Ca²⁺ mitigates salinity stress, including its role in maintaining membrane integrity, regulating ion transport, preserving Na⁺/K⁺ homeostasis, and activating the Salt Overly Sensitive (SOS) signaling pathway. Particular emphasis is placed on calcium-mediated regulation of antioxidant defense systems, osmo-protectant accumulation (such as proline, glycine betaine, and soluble sugars), and the biosynthesis of secondary metabolites, including phenolics and flavonoids that contribute to stress adaptation. Furthermore, the review highlights the intricate crosstalk between Ca²⁺ signaling and phytohormones, including abscisic acid, salicylic acid, jasmonic acid, ethylene, and auxin, which collectively coordinate plant responses to saline environments. Recent advances in understanding calcium-dependent signaling networks, transcriptional regulation, and reactive oxygen species (ROS) interactions are also discussed. In addition, the practical applications of calcium-based amendments, foliar sprays, and nutrient management strategies for improving crop performance under saline conditions are evaluated. Despite significant progress, challenges related to signaling specificity, ion interactions, and field-level implementation remain. A deeper understanding of calcium-mediated stress responses will facilitate the development of innovative strategies to enhance crop resilience and sustain agricultural productivity in salt-affected ecosystems.