Unveiling root morpho-anatomical traits driving tolerance to waterlogging, salinity, and their combination in Festuca arundinacea

Understanding root traits that confer tolerance to multiple abiotic stresses is key to improving forage crop resilience. This study evaluated morpho-anatomical root traits associated with tolerance to waterlogging (W), salinity (S), and their combination (SW) in ten tall fescue (Festuca arundinacea) accessions. Tolerance index (TI) was positively correlated with new root formation and root length under all stress types, and with root porosity under SW. The most tolerant accession, Temora, exhibited pronounced plasticity: increased aerenchyma and cortex area under W, reduced xylem vessel area under S, and a combination of both responses under SW. Anatomical plasticity was closely associated with improved stress tolerance. Moreover, root porosity and aerenchyma were positively correlated, although differences in porosity between accessions for a given aerenchyma value suggest functional variability in internal aeration. These findings highlight that both constitutive traits (e.g. baseline porosity) and plastic responses (e.g. aerenchyma development, vessel adjustment) underpin stress tolerance in tall fescue. The results provide novel evidence of trait-specific contributions under different stress scenarios, offering useful selection criteria for breeding programs targeting complex environmental conditions.