Integrated comparison of root ion flux dynamics, shoot ionic status, and root anatomy underlies contrasting salinity...

Salinity is a major abiotic threat on plant productivity and biodiversity worldwide, particularly in degraded soils and grass-dominated coastal ecosystems. Identifying species-specific physiological mechanisms underlying salinity tolerance is essential for selecting resilient crop and forage grasses. However, the integrated analysis of root ion fluxes, shoot ionic balance, and root anatomy within a physiological framework in grasses under salt stress remains insufficiently understood. To address this gap, we compared three grass species-Lolium perenne, Festuca rubra, and Puccinellia maritima-to determine how root ion flux dynamics, shoot ionic status, and root anatomical traits contribute to contrasting salinity responses. The results reveal species-specific patterns in ion flux response to salt stress, underscoring contrasting strategies for K⁺ retention and H⁺ dynamics. P. maritima showed high K⁺ retention with minimal loss and stable H⁺ dynamic following salt exposure, whereas L. perenne exhibited pronounced and sustained K⁺ leakage alongside strong perturbations in H⁺ flux. F. rubra showed transient ion flux disturbances with partial recovery from K⁺ loss. These root-level responses were closely linked to shoot ionic status: L. perenne accumulated substantial NaCl-derived osmolarity in leaves, whereas leaf osmolarity in P. maritima and F. rubra remained comparatively low even under high salinity. Furthermore, root anatomical observation revealed earlier and more extensive suberization in P. maritima, with limited development in F. rubra. These structural differences provide a mechanistic context for the observed variations in ion behavior, offering insights into species-specific adaptations to salt stress. Collectively, these findings indicate that effective salinity tolerance in grasses is closely associated with coordinated regulation of root ion fluxes, restricted salt accumulation in shoot, and the presence of supportive anatomical features, characteristics exemplified by P. martima. This study highlights the importance of integrative analysis within the physiological framework for identifying salt-resilient grasses. Such a comprehensive and efficient screening approach is crucial for advancing sustainable agriculture and facilitating ecosystem restoration in saline environments.