Salinity-induced changes in the rhizosphere microbiome improve salt tolerance of Hibiscus hamabo

Aims We aimed to assess whether soil salinity changes the microbial community in the rhizosphere of Hibiscus hamabo, and whether these changes in the microbiome feedback on the growth of H. hamabo. Methods To test effects of salinity on the rhizosphere microbiome, we first did a greenhouse experiment in which H. hamabo was grown in pots with a sand-soil mixture at different salt concentrations (0, 15, 40 and 90 mM NaCl). Then in another two experiments, we tested effects of the rhizosphere microbiomes on performance of H. hamabo plants by sowing and growing them in pots with a peat-sand-vermiculite mixture inoculated with either soil or root fragments collected from the different salinity treatments (0, 40 and 90 mM NaCl) of the first experiment and crossed with a salinity treatment (0, 40 and 90 mM NaCl). Results The bacterial rhizosphere community of H. hamabo was less affected by soil salinities than the fungal community was. Germination and biomass of H. hamabo were highest at a salinity of 40 mM NaCl, and higher in the presence than in the absence of microbial inoculums. Moreover, H. hamabo performed best when the microbial inocula came from the same salinity level, particularly at a salinity of 40 mM NaCl. Conclusions Our study provides evidence that salinity-induced changes in rhizosphere microbial communities tend to promote germination and growth of H. hamabo at the respective salinities.