Effects of soil type and salinity levels on the performance and bacteriome of the halophyte Atriplex nummularia (old man saltbush)

Background Soil salinization has a major impact on crop production and it is expected to increase in area in the coming years. In this scenario, exploring the potential of halophytes and their plant-associated microbiomes as to increase phytoremediation strategies represents a suitable and sustainable strategy. Methods We conducted a microcosm experiment with the halophyte Atriplex nummularia, cultivating it in two contrasting soils (clay and sandy) at distinct levels of salinity (0, 10 and 20 mS/cm). After 109 days, we assessed its growth and bacteriome composition, through 16S rRNA gene sequencing of the leaf and root endospheres, as well as rhizosphere. Results A. nummularia showed increased growth under salinity levels of up to 20 mS/cm in both soils. Salinity and soil type had an effect in determining the rhizosphere bacterial communities of A. nummularia, with a stronger signal in the sandy soil. Most interestingly, no differences were found in endophytic bacterial communities, suggesting a strong buffering effect of the plant physiology, even though this halophyte accumulates NaCl. Last, functional prediction based on a subset of differentially abundant taxa in the rhizosphere revealed an increase in plant-growth promotion and salinity tolerance traits in higher salinity, indicating simultaneous selection by salinity and A. nummularia under stress. Conclusion Collectively, these results provide valuable insights into halophyte-associated bacteria, advancing our understanding of this complex system with potential application in phytoremediation strategies for saline soils.