Conditions for vegetative propagation of three key halophytes from habitats of EU community interest: substrate nature, salinity and PGP-bacterial interactions and cost evaluation

The ecological transition faces the challenge of expanding wetland restoration areas due to their critical role in ecosystem service provision. To improve restoration efforts, particularly in plant material production for revegetation, scientific knowledge is essential. This study focuses on establishing optimal vegetative propagation protocols for three slow-growing, perennial halophyte species from EU habitats of interest: Atriplex portulacoides, Arthrocaulon macrostachyum and Sporobolus maritimus. Cuttings were grown in three substrates (perlite, coconut fiber and mulch) with two salinity levels (0 and 171 mM NaCl) and three inoculation treatments (non-inoculated and inoculated with two plant growth-promoting (PGP) rhizobacteria consortia). Cuttings survival rate was species-specific, with A. portulacoides showing the highest survival range (78.75 ± 18.75) compared to the ranges observed for A. macrostachyum and S. maritimus (57.50 ± 12.50 \% and 59.60 ± 9.00 \%, respectively). Plants grown with coconut fiber performed best survival rate, followed by perlite independently of inoculation. Moreover, survival rates of S. maritimus were also enhanced by PGP inoculation. Similar patterns were observed for cutting development: cuttings grown in perlite, followed by coconut fiber, and exposed to high salinity showed higher above- and belowground biomass. By selecting this Substrate and Salinity, Inoculum had a positive effect on the development of A. portulacoides and A. macrostachyum. Furthermore, inoculated plants showed overall higher values of photosynthetic efficiency and carboxylation. Finally, a cost analysis comparing our approach to using direct transplant material indicates significant economic advantages. Our results provide compelling evidence to enhance nursery stock for future revegetation projects.