Halophilic Bacillus improve barley growth on calcareous soil via enhanced photosynthetic performance and metabolomic...

Plant Growth Promoting Rhizobacteria are a sustainable biological alternative to agrochemicals to improve plant growth and stress tolerance. In this work we used two Bacillus strains native to the saline rhizosphere of halophytic plants in order to improve the growth of barley on a calcareous soil (CS). This soil negatively affected plant development; however, the inoculation of barley with the halophytic Bacillus strains enhanced barley growth and photosynthesis performance. In fact, a significant increase of the maximum photochemical yield of PSII and PSI was observed following inoculation, leading to improved protection of these photosystems against photoinhibition. Moreover, a pairwise metabolomic pathway analysis in barley leaves and roots was performed. Compared to barley grown on non-calcareous soil (NCS), CS led to a downregulation of sugar-related metabolic pathways, which can be correlated with lower photosynthesis performance. Furthermore, the abundance of metabolites related to amino acids in leaves and phenylpropanoids and lipids in roots was also reduced by CS. This negative effect was reverted by the inoculation of the bacteria strains. In conclusion, halophilic Bacillus native to the saline rhizosphere of halophyte plants induced metabolic changes leading to an enhanced photosynthesis activity, and hence, alleviating the deleterious effect of CS on barley development.