## 4 Discussion
The present study demonstrated that the application of salinity significantly reduced the contents of total chlorophylls, carotenoids and chlorophylls a and b. This reduction might have been caused by chlorophyll-degrading enzymes, such as chlorophyllases. Similar results were found in maize [61; 62; 63], radishes [64] and the date palm [65]. In the same way, [PERSON] et al. [66] have shown that organic amendment and AMF reduced the decline in photosynthesis induced by abiotic stress by improving the synthesis of chlorophyll pigments. Similarly, [PERSON] et al. [67] reported that the inoculation of AMF and PGPR increases plant tolerance to salt stress through higher chlorophyll content and a stronger antioxidant defense system. The synergistic effect of AMF, PGPR and compost might have resulted from the fact that AMF improves the ability of plants to acquire nutrients derived from compost. Indeed, the hyphae of AMF increase the absorption of nutrients such as magnesium, which increases the total chlorophyll content in mycorrhizal plants [68]. Our data indicated that the concentrations of soluble sugars and protein increased during salt stress in treated plants compared to control plants. The better results were recorded when the biofertilizers were applied in combination, especially PGPR+AMF\({}_{1}\)+Comp and PGPR+AMF\({}_{2}\)+Comp treatments. Plants can tolerate salt stress by modifying the biochemical responses via improving the biosynthesis of metabolites such as sugars. [PERSON] et al. [69] observed that the use of AMF and compost improved plant quality by improving their biochemical composition via increases in sugar and protein contents. Previous studies have shown that genes related to sugar metabolism tend to be enriched in plants treated with beneficial microbes under abiotic stress [70]. In the present study, SOD, CAT, POD and PPO activities increased under salt stress but this decrease was anticipated by the application of biofertilizers. Indeed, the selected biofertilizers could promote antioxidant enzyme activities as a protective strategy [20]. It is well documented that salt stress increases ROS in plants, resulting in oxidative stress [8; 34]. Plants possess several antioxidant mechanisms to protect themselves against ROS. SOD is the first enzyme of defense that catalyzes the transformation of O\({}_{2}\)\({}^{-}\) into H\({}_{2}\)O\({}_{2}\) and O\({}_{2}\). APX and CAT act to convert H\({}_{2}\)O\({}_{2}\) into water and oxygen [71]. Our results showed significant increases in POD and PPO in plants subjected to salt stress and inoculated with PGPR and AMF and/or amended with compost compared to control plants. Several studies suggested that PGPR have the potential to increase tolerance to salinity by improving the stability and plasticity of plant cell membranes by activating the antioxidant defense system. The application of compost and the inoculation with AMF and PGPR might alleviate or decrease RNA disassembly and might enhance the ability of the non-enzymatic antioxidant defense system using soluble proteins [72]. Our study revealed the amelioration of soil physicochemical properties after harvest. Under salt stress the application of biofertilizers, compost mainly increased soil quality, such as OM and P content, compared to the controls. After the compost application, the decrease of soil pH can be attributed to the mineralization of the organic matter and the release of CO\({}_{2}\). Soil pH plays an important role in the mobility and availability of nutrients [73]. In addition, in the absence of salt stress, the TOC rate was reduced by half in pots treated by the bipartite combination of AMF and PGPR compared to the non-inoculated control. [PERSON] et al. [74] showed that the application of organic amendments increased the microbial activity of the soil. Significant increments in the OM and available P, especially with the application of compost alone or in combined use with PGPR or AMF, were noted and resulted from the high content of OM and available P in the compost.