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.