Plant Growth-Promoting Rhizobacteria Alleviate High Salinity Impact on the Halophyte Suaeda fruticosa by Modulating Antioxidant Defense and Soil Biological Activity

Rabaa Hidri; Ouissal Metoui-Ben Mahmoud; Walid Zorrig; Henda Mahmoudi; Abderrazak Smaoui; Chedly Abdelly; Rosario Azcon; Ahmed Debez

doi:10.3389/fpls.2022.821475

Plant Growth-Promoting Rhizobacteria Alleviate High Salinity Impact on the Halophyte Suaeda fruticosa by Modulating Antioxidant Defense and Soil Biological Activity

Front Plant Sci. 2022 May 26:13:821475. doi: 10.3389/fpls.2022.821475. eCollection 2022.

Authors

Rabaa Hidri¹, Ouissal Metoui-Ben Mahmoud¹, Walid Zorrig¹, Henda Mahmoudi², Abderrazak Smaoui¹, Chedly Abdelly¹, Rosario Azcon³, Ahmed Debez¹

Affiliations

¹ Laboratory of Extremophile Plants, Centre of Biotechnology of Borj Cedria, Hammam-Lif, Tunisia.
² International Center for Biosaline Agriculture, Academic City, United Arab Emirates.
³ Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain.

Abstract

Plant growth-promoting rhizobacteria (PGPR) are considered as bio-ameliorators that confer better salt resistance to host plants while improving soil biological activity. Despite their importance, data about the likely synergisms between PGPR and halophytes in their native environments are scarce. The objective of this study was to assess the effect of PGPR (Glutamicibacter sp. and Pseudomonas sp.) inoculation on biomass, nutrient uptake, and antioxidant enzymes of Suaeda fruticosa, an obligate halophyte native in salt marshes and arid areas in Tunisia. Besides, the activity of rhizospheric soil enzyme activities upon plant inoculation was determined. Plants were grown in pots filled with soil and irrigated with 600 mM NaCl for 1 month. Inoculation (either with Pseudomonas sp. or Glutamicibacter sp.) resulted in significantly higher shoot dry weight and less accumulation of Na⁺ and Cl^- in shoots of salt-treated plants. Glutamicibacter sp. inoculation significantly reduced malondialdehyde (MDA) concentration, while increasing the activity of antioxidant enzymes (superoxide dismutase; catalase; ascorbate peroxidase; and glutathione reductase) by up to 100%. This provides strong arguments in favor of a boosting effect of this strain on S. fruticosa challenged with high salinity. Pseudomonas sp. inoculation increased shoot K⁺ and Ca²⁺ content and lowered shoot MDA concentration. Regarding the soil biological activity, Pseudomonas sp. significantly enhanced the activities of three rhizospheric soil enzymes (urease, ß-glucosidase, and dehydrogenase) as compared to their respective non-inoculated saline treatment. Hence, Pseudomonas sp. could have a great potential to be used as bio-inoculants in order to improve plant growth and soil nutrient uptake under salt stress. Indole-3-acetic acid concentration in the soil increased in both bacterial treatments under saline conditions, especially with Glutamicibacter sp. (up to +214%). As a whole, Glutamicibacter sp. and Pseudomonas sp. strains are promising candidates as part of biological solutions aiming at the phytoremediation and reclamation of saline-degraded areas.

Keywords: PGPR; Suaeda fruticosa; antioxidant enzymes; mineral nutrition; salt stress; soil enzymes.