Understanding the primary mechanisms for plant promotion under salt stress with plant growth promoting rhizobacteria (PGPR) inoculation of different salt-tolerant plant groups would be conducive to using PGPR efficiently. We conducted a meta-analysis to evaluate plant growth promotion and uncover its underlying mechanisms in salt-sensitive plants (SSP) and salt-tolerant plants (STP) with PGPR inoculation under salt stress. PGPR inoculation decreased proline, sodium ion (Na⁺) and malondialdehyde but increased plant biomass, nutrient acquisition (nitrogen, phosphorus, potassium ion (K⁺), calcium ion (Ca²⁺), and magnesium ion (Mg²⁺)), ion homeostasis (K⁺/Na⁺ ratio, Ca²⁺/Na⁺ ratio, and Mg²⁺/Na⁺ ratio), osmolytes accumulation (soluble sugar and soluble protein), antioxidants (superoxide dismutase), and photosynthesis (chlorophyll, carotenoid, and photosynthetic rate) in both SSP and STP. The effect size of total biomass positively correlated with the effect sizes of nutrient acquisition and the homeostasis of K⁺/Na⁺, and negatively correlated with the effect size of malondialdehyde in both SSP and STP. The effect size of total biomass also positively correlated with the effect sizes of carotenoid and the homeostasis in Ca²⁺/Na⁺ and Mg²⁺/Na⁺ and negatively correlated with the effect size of Na⁺ in SSP, but it only negatively correlated with the effect size of Ca²⁺ in STP. Our results suggest that the plant growth improvement depends on the nutrient acquisition enhancement in both SSP and STP, while ion homeostasis plays an important role and carotenoid may promote plant growth through protecting photosynthesis, reducing oxidative damage and promoting nutrient acquisition only in SSP after PGPR inoculation under salt stress.

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are considered highly-efficient agents for conferring salt tolerance in host plants and improving soil fertility in rhizosphere. However, information about the inoculation of beneficial microbes on halophytes in arid and semi-arid regions remains inadequate. The objective of this study was to evaluate the influence of AMF (Glomus mosseae) inoculation, alone or in combination with PGPR (Bacillus amyloliquefaciens), on biomass accumulation, morphological characteristics, photosynthetic capacity, and rhizospheric soil enzyme activities of Elaeagnus angustifolia L., a typical halophyte in the northwest of China. The results indicate that, for one-year-old seedlings of Elaeagnus angustifolia L., AMF significantly promoted biomass accumulation in aboveground organs, increased the numbers of leaves and branches, and improved the leaf areas, stem diameters and plant height. AMF-mediated morphological characteristics of aboveground organs favored light interception and absorption and maximized the capacities for photosynthesis, transpiration, carbon dioxide assimilation and gas exchange of Elaeagnus angustifolia L. seedlings in saline soil. AMF also promoted root growth, modified root architecture, and enhanced soil enzyme activities. Elaeagnus angustifolia L. was more responsive to specific inoculation by AMF than by a combination of AMF and PGPR or by solely PGPR in saline soils. Therefore, we suggest that G. mosseae can be used in saline soil to enhance Elaeagnus angustifolia L. seedlings growth and improve soil nutrient uptake. This represents a biological technique to aid in restoration of saline-degraded areas.

Alfalfa (Medicago sativa L.), a forage legume known for its moderate salt–alkali tolerance, offers notable economic and ecological benefits and aids in soil amelioration when cultivated in saline–alkaline soils. Nonetheless, the limited stress resistance of alfalfa could curtail its productivity. This study investigated the salt tolerance and growth-promoting characteristics (in vitro) of four strains of plant growth-promoting rhizobacteria (PGPR) that were pre-selected, as well as their effects on alfalfa at different growth stages (a pot experiment). The results showed that the selected strains belonged to the genera Priestia (HL3), Bacillus (HL6 and HG12), and Paenibacillus (HG24). All four strains exhibited the ability to solubilize phosphate and produce indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Among them, except for strain HG24, the other strains could tolerate 9% NaCl stress. Treatment with 100 mM NaCl consistently decreased the IAA production levels of the selected strains, but inconsistent changes (either enhanced or reduced) in terms of phosphate solubilization, ACC deaminase, and exopolysaccharides (EPS) production were observed among the strains. During the various growth stages of alfalfa, PGPR exhibited different growth-promoting effects: at the seedling stage, they enhanced salt tolerance through the induction of physiological changes; at the flowering stage, they promoted growth through nutrient acquisition. The current findings suggest that strains HL3, HL6, and HG12 are effective microbial inoculants for alleviating salt stress in alfalfa plants in arid and semi-arid regions. This study not only reveals the potential of indigenous salt-tolerant PGPR in enhancing the salt tolerance of alfalfa but also provides new insights into the mechanisms of action of PGPR.

As a primary form of land degradation in arid and semi-arid areas, soil salinity can adversely affect plant nutrient balance, photosynthesis, protein synthesis, energy metabolism, and other functions. Plant growth-promoting rhizobacteria (PGPR) inoculation of plants is an environmentally friendly strategy to alleviate salt stress and improve salt tolerance. Based on the Web of Science Core Collection (WoSCC) database, in terms of the number of publications and citations, collaboration networks, and keywords, this bibliometric analysis employed VOSviewer 1.6.17 and HistCite Pro 2.1 software to map the scientific knowledge of related research, comprehensively review knowledge structure and provide an outlook on future research topics. The results showed that publications and citations increased exponentially between 1978 and 2021. Regarding knowledge structure, Asian nations conducted research in a more concentrated manner, developed close collaborative relationships, and produced rich research results. Halotolerant PGPR, sustainable agriculture, microbial community, soil salinization, microbiome, oxidative stress, and biofertilizer, are currently hot topics. This bibliometric study will provide a meaningful reference for investigating the field’s evolution and pinpointing the research frontiers.

Increasing salinization threatens the normal growth of halophytes in saline habitats, especially at the seedling stage. Soil beneficial microorganisms have the potential to promote salt tolerance of halophytes, but less attention has been paid to the various responses between different halophytes with microbial inoculations. Here we performed pot experiments to assess the responses of Nitraria tangutorum Bobr. and Elaeagnus angustifolia Linn. to arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) inoculation in saline soil conditions. The results showed that neither a single AMF inoculation nor a single PGPR inoculation promoted the growth of N. tangutorum. In contrast, co-inoculation not only promoted biomass accumulation but also promoted the absorption of P, K⁺, and Ca²⁺ in the roots, and the accumulation of N, Na⁺, K⁺, and Ca²⁺ in the leaves. Co-inoculation also increased the K⁺/Na⁺ ratio in the roots as well as the Ca²⁺/Na⁺ ratio in both roots and leaves of N. tangutorum. Na⁺ is an important inorganic osmolyte, essential for both efficient osmoregulation and biomass accumulation in N. tangutorum. PGPR inoculation alone could not promote the growth of E. angustifolia. AMF inoculation, solely or combined with PGPR, was beneficial to the absorption of K⁺ and Ca²⁺ in the roots, the accumulation of N and K⁺ in the leaves, the maintenance of the K⁺/Na⁺ ratio and Ca²⁺/Na⁺ ratio in the leaves, the selective transportation of K⁺ and Ca²⁺ from roots to leaves, and the accumulation of proline and glycine betaine in the leaves of E. angustifolia. Increased nutrient absorption, ion homeostasis, and K⁺ and Ca²⁺ selective transportation in AMF-inoculated E. angustifolia helped reduce the toxic effects of Na⁺ and the damage caused by osmotic stress in saline soil conditions. “Plant-microbe specificity” leads to the different responses of N. tangutorum and E. angustifolia seedlings to AMF and PGPR inoculation in saline soil conditions. The different salt tolerance strategies for osmoregulation, nutrient acquisition, ion homeostasis, and ion transportation determine the differential responses in N. tangutorum and E.angustifolia to AMF and PGPR inoculations under saline soil conditions.

Arbuscular mycorrhizal fungi (AMF) colonize land plants in almost every ecosystem, even in extreme conditions, such as saline soils. In the present work, we report the mycorrhizal capacity of rhizosphere soils collected in the dry desert region of the Minqin Oasis, located in the northwest of China (Gansu province), which is characterized by several halophytes. Lycium spp. and Peganum nigellastrum were used as trap plants in a greenhouse experiment to identify autochthonous AMF associated with the halophytes’ rhizospheres. Morphological observations showed the typical AMF structures inside roots. Twenty-six molecularly distinct AMF taxa were recovered from soil and root DNA. The taxonomical diversity mirrors the several AMF adapted to extreme environmental conditions, such as the saline soil of central China. Knowledge of the AMF associated with halophytes may contribute to select specific fungal isolates to set up agriculture strategies for protecting non-halophyte crop plants in saline soils.