Background and aims <p>Soil salinity leads to oxidative stress by increasing production of reactive oxygen species (ROS). At the same time, stress-induced ROS signalling may play an important adaptive role, alongside cytosolic calcium ([Ca²⁺]_cyt) signalling. However, little is known about the interaction between ROS and [Ca²⁺]_cyt signalling as a determinant of differential salinity stress tolerance between halophytes and glycophytes.</p> Methods <p>The spatiotemporal dynamics of Ca²⁺&#xa0;signalling in the elongation and mature zones of quinoa (halophyte) and spinach (glycophyte) roots in response to NaCl and H₂O₂ stress was examined using fluorescence Ca²⁺&#xa0;imaging, non-invasive microelectrode Ca²⁺&#xa0;flux measurements, and expression analysis of Ca²⁺-related genes.</p> Results <p>Quinoa maintained higher root cell viability and was less affected by both NaCl and H₂O₂ stresses. This different response was achieved by several complementary mechanisms associated with Ca²⁺ signalling, including (i) tissue-specific Ca²⁺ flux patterns in quinoa, followed by (ii) differential induction of Ca²⁺&#xa0;transporters (e.g. <i>CAX</i> and <i>ACA</i>) and Ca²⁺ sensors (<i>CBLs; CIPKs</i>) for regulating cytosolic Ca²⁺ concentration<i>.</i> Also contributing were more efficient upregulation of the <i>SOS1-</i>mediated Na⁺ exclusion system and higher ROS scavenging in quinoa.</p> Conclusions <p>The quinoa's superior salinity tolerance is conferred by its ability to orchestrate precise spatiotemporal control of the ROS-Ca²⁺&#xa0;hub, leading to efficient stress signaling and mitigation. Future work should focus on the functional validation of these candidate genes (e.g., <i>ANNEXIN1</i>, <i>CBL-CIPK</i> networks) in model and crop plants under field conditions.</p>