Puccinellia tenuiflora as a Pioneer Grass Species for Saline–Alkali Land Restoration: Adaptive Mechanisms and Post-Restoration Forage Utilization Potential

Puccinellia tenuiflora is a perennial halophytic grass commonly regarded as a pioneer species for the ecological restoration of saline–alkali land. Its adaptive capacity and subsequent utilization value are shaped by interacting structural, physiological, molecular, ecological, and management-related factors. This review summarizes recent studies on saline–alkali tolerance in P. tenuiflora, with emphasis on root structural barriers, Na+/K+ homeostasis, osmotic adjustment, organic-acid metabolism, antioxidant defense, ion transport, and multi-omics regulation. To better understand the integrated stress response, we propose a functional framework that distinguishes first-line defenses from downstream cellular repair mechanisms. First-line defenses include root apoplastic barriers (Casparian strips and suberization) that restrict Na+ entry, plasma-membrane Na+/H+ antiporters (e.g., SOS1) that mediate active Na+ exclusion, and K+-retention mechanisms (e.g., AKT1, HKT2;1) that preserve cytosolic K+/Na+ homeostasis—these operate rapidly to prevent ion imbalance at the onset of stress. Downstream repair and acclimation mechanisms include osmotic adjustment via compatible solutes (e.g., proline, glycine betaine), organic-acid accumulation (especially citric acid) for pH regulation and chelation, ROS scavenging systems, and proteomic/phosphoproteomic reprogramming that repair stress-induced damage and restore metabolic balance. Furthermore, saline–alkali stress involves both short-term osmotic shock and long-term ionic toxicity, and available evidence suggests a temporal shift in the relative importance of these mechanisms: osmotic adjustment and rapid ion exclusion dominate during the initial hours to days of stress, whereas organic-acid metabolism, ROS buffering, and molecular reprogramming become increasingly important during prolonged exposure, sustaining tissue integrity and enabling long-term persistence. Current evidence indicates that saline–alkali tolerance in P. tenuiflora results from the combined action of several processes, including restricted Na+ entry, K+ retention, organic-acid accumulation, reactive oxygen species homeostasis, and organ-specific molecular responses. This review also discusses the significance of P. tenuiflora in community establishment, saline–alkali land restoration, and post-restoration forage utilization. Field studies and limited feeding trials suggest that P. tenuiflora can provide biomass and utilization potential after community stabilization. However, based on current evidence, it is more appropriate to define its forage value as a post-restoration utilization extension rather than as that of a fully developed specialized forage crop. Further studies are required on nutritional quality, mineral-element safety, long-term field management, and animal feeding validation.