## 4 Discussions  
Plant-associated microbial communities, and especially halotolerant PGPB (Plant Growth-Promoting Bacteria), contribute to the adaptation of the hosts to the dynamic and challenging conditions of coastal salt marsh ecosystems [1; 60]. It is also well known that plant species and sediment properties interact in shaping the composition and structure of rhizosphere and root microbiomes [57; 58]. This work intended to address the hypothesis that the effect of sediment properties also imprints the diversity of PGP isolates and the prevailing PGP mechanisms in different populations of the same species. The halophyte _S. ramossissima_, very well represented in European salt marshes, was chosen as the model species. The rhizosphere and root endosphere microbiomes of plants growing in five distinct salt marshes were screened for PGP bacteria. The composition and PGP potential of the subsets of isolates from each site were analyzed in relation to the physico-chemical descriptors of sediment and pore water. Sediments of the five sampling sites were all strongly saline (Table 1) but differed greatly in their salinity levels, pH, sodium-related parameters like SAR and ESP, concentration of exchangeable cations and organic matter content (Table 1). Although soil salinity has been shown to decrease bacterial diversity in rhizospheres [61], in this study, the greater diversity of culturable halotolerant bacteria associated with the roots of _S. ramossissima_ was observed in the most saline sediments of Ria de Aveiro saltmarashes (Av1 and Av2). The lowest diversity was found in the subset of isolates retrieved from the southernmost site (Al), on the southern Atlantic coast (Algarve), where the salinity indicators were the lowest. The plants collected from this site already had their color changed from green to red, indicating that they were either experiencing abiotic stress or senescence. This could explain the lower taxonomic diversity of the cultivable bacterial community found at this site. Salinity, however, seems to be neither the sole nor even the most relevant determinant of the diversity of isolated halotolerant bacteria. NMD analysis (Figure 3) indicates that the composition of the subsets of PGP bacteria corresponding to different salt marshes within the same estuarine system (Ria de Aveiro) was related also to different sediment parameters. Neutral pH is more strongly related to the composition of Av1 and Tg subsets. The overall concentration of exchangeable cations and the parameters determined for soil sodicity (SAR and ESP) seemed to influence the bacterial composition in Av2, and the higher content of organic matter determined bacterial diversity in Av3. As a consequence of the effect of different sediment properties, there was a significant variability in the composition of the sets of isolates obtained from plants growing in different sites. In fact, the structure of the subset of isolates from site Av1 was more similar to the subset corresponding to geographically distant saltmarashes (Al and Tg) than to the other two sites of the estuarine system of Ria de Aveiro (Figure 2; Appendix A, Figure A1), which confirms that site-specific factors related to sediment properties may have a major impact on the outcome of the culture-dependent approaches used to prospect the microbiome of halophyte species for bacteria with PGP potential. The identification at the phylum level revealed the overall dominance of Firmicutes in the collection of isolates, followed by Proteobacteria and Actinobacteria. These results are in line with reports of culture-dependent analyses of the root microbiomes of other species of _Salicornia_ included in the _S. europaea_ aggregate [36]. However, cultivable bacteria are estimated to represent only 0.01-1% of the total microbial species present in a given environment [21; 23; 62]. Despite this, culture-independent approaches, as performed by [21], contribute to better resolution of the bacterial communities associated with plants.