Salt stress responses are not salt tolerance: Re-examining a foundational assumption of plant stress biology.

For decades, salinity research has sought to identify the molecular determinants of salt tolerance by comparing plants under non-saline and saline conditions. This strategy has profoundly advanced our understanding of stress sensing, signalling, and physiological responses. However, the persistent gap between the discovery of salt-responsive genes and the development of crops with improved field performance suggests a need to reconsider how stress responses are interpreted in relation to tolerance. I argue that salinity does not activate a single "tolerance programme". Rather, salt tolerance is an emergent performance outcome arising from the integrated action of multiple physiological and developmental processes that sustain growth, reproduction, and recovery across variable saline environments. Consequently, the magnitude of a plant's response to salinity does not necessarily reflect its capacity to maintain performance and may itself depend on the experimental context. This perspective proposes that binary stress-control experiments remain valuable for uncovering mechanisms of environmental responsiveness but should increasingly be complemented by experimental frameworks that evaluate performance across environmental gradients, developmental stages, and recovery phases. Such a framework aligns stress biology more closely with ecological reality and the mechanisms that ultimately determine agricultural performance.