## 4 Discussion  
The potential roles of AMF, PGPR and compost in improving the tolerance of date palm vitroplants to salt stress were investigated. We carried out this work to study the impacts of biofertilizers alone, in double or in triple combination on the morphological, physiological and biochemical parameters of date palm vitroplants exposed to salt stress. Figure 5: The principal component analysis (PCA), Comp: compost; AMF\({}_{1}\): AMF consortium; AMF\({}_{2}\): AMF pure strain; PGPR: plant growth promoting rhizobacteria; PH: plant height; LN: leaf number; SFW: shoot fresh weight; SDW: shoot dry weight; RFW: root fresh weight; RDW: root dry weight; Fv/Fm: chlorophyll fluorescence; gs: gas exchange; \(\Psi\): leaf water potential; F\(\%\): mycorrhizal frequency; I\(\%\): mycorrhizal intensity; Chla: chlorophyll a; Chlb: chlorophyll b; PPO: polyphenoxidase; POD: peroxidase; CAT: catalase; SOD: superoxided dismutase; EC: electrical conductivity; TOC: total organic carbon; OM: organic matter; P: soil P\({}_{\mathrm{olsen}}\). Our results showed that the dual inoculation of plants with AMF and PGPR further increased root colonization. These results are in accordance with those obtained by [PERSON] et al. [49] and [PERSON] et al. [50], who found that inoculation with PGPR significantly stimulates AMF colonization of plants compared to non-inoculated plants. However, the AMF colonization of date palm plants was reduced by salt stress, especially at 240 mM NaCl. The same results were reported by [PERSON] et al. [7], [PERSON] et al. [51] and [PERSON] et al. [6] under salt stress. In our study, we observed that salinity causes a considerable decrease in crop biomass. Biofertilizer application alone or in combination improved the studied growth parameters plant height; leaf number, and fresh and dry weights of shoots and roots. The best results were obtained when biofertilizers were applied in tripartite combination either in the presence or in the absence of salt stress. [PERSON] [52] illustrated that in the interactions between plants and biological fertilizers such as AMF, PGPR and compost--the different partners--benefit from this mutualistic association. Several studies have shown that the use of PGPR has a positive effect on the growth and tolerance of plants to salt stress [53; 54]. Thus, in this study, the increased plant biomass maybe attributed to the growth-promoting mechanisms used by microorganisms such as the production of phytohormones and mineral solubilization. Furthermore, AMF have the ability to improve plant growth by developing external hyphae that can extend the surrounding soil masse [55]. Besides, AMF have been shown to alleviate salt stress by improving nutrient acquisition, especially by reducing the uptake of sodium and chlorine, enhancing water uptake [8; 34; 56]. Moreover, the application of organic amendments to soils such as compost represents a valuable agricultural practice, as it improves plant growth by increasing the availability of nutrients in soils such as phosphorus, calcium, nitrogen and potassium [57]. Beneficial effects of AMF, PGPR and compost on growth responses in plants under salt stress have also been found in alfalfa [34], tomato [58] and corn [59]. Our results showed that salinity reduced physiological parameters such as leaf water potential, stomatal conductance and chlorophyll pigment content. Similar results were reported by [PERSON] et al. [6; 8] in date palm and [PERSON] et al. [34] in alfalfa. Indeed, salt stress reduces available water to plants and causes leaf stomata closure, which limits the assimilation of CO\({}_{2}\) and subsequently the disruption of photosynthetic activity. However, the application of biofertilizers improved the physiological parameters studied under both saline and non-saline conditions. Similarly, several studies have demonstrated that the dual or triple combination of AMF, compost and PGPR has a strong capacity to reduce the negative effects of salt stress on plant growth, by improving photosynthesis and water status [34; 56; 60].