Native biocrust microbes modulate salinity‐driven recruitment filters in coastal wetlands

Introduction: Mediterranean coastal wetlands are biodiversity hotspots increasingly threatened by climate change, particularly by salinization, which strongly constrains plant recruitment during early life stages. Native soil microbiota may provide nature-based solutions (NbS) to enhance plant establishment under saline conditions. Objectives: We evaluated microbial seed biopriming with native biocrust-derived microorganisms to improve germination and early seedling development of three Mediterranean wetland species differing in salinity tolerance, that is, Arthrocaulon meridionale, Juncus acutus, and Mentha aquatica. Methods: Four microbial strains were isolated and selected based on salinity tolerance and plant growth-promoting traits: Nodosilinea ramsarensis (cyanobacteria), Bacillus licheniformis, Fredinandcohnia salidurans, and Rossellomorea aquimaris (bacteria). Their effects were assessed on bioprimed seeds, exposed to increasing NaCl concentrations (0, 0.3, 0.5, and 0.7 M) under controlled conditions. Results: Salinity primarily defined germination limits, producing threshold-like and species-specific responses and delayed germination with increasing concentrations. Microbial treatments accelerated germination only where salinity did not fully constrain the process. Cyanobacterial biopriming enhanced germination and enabled germination at the highest salinity levels in A. meridionale and J. acutus, whereas M. aquatica did not germinate under saline conditions. Cyanobacteria also consistently promoted longer roots across species under non-saline and moderately saline conditions. Conclusions: Salinity defines the recruitment niche of Mediterranean wetland plants, while native microbial inoculation, particularly cyanobacteria, acts as a secondary modulator enhancing establishment within these limits. Microbial biopriming thus represents a context-dependent NbS for ecological restoration under increasing salinization.