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Because of global warming, desertification is increasing. One of the best strategies for combating desertification is reforestation of forests and biological operations of vegetation. However, events like soil salinity and dust storms, as the most important manifestations of desertification, prevent vegetation from settling in these areas. In this study, the effects of two halotolerant plant growth-promoting rhizobacterial strains, Bacillus pumilus HR and Zhihengliuella halotolerans SB, on physiological and nutritional status of the desert halophyte Haloxylon aphyllum under the stress of salinity (0, 300, and 600 mM NaCl) and dust (0 and 1.5 g m−2 month−1) were examined. Under dust application, the Z. halotolerans SB strain compared to the B. pumilus HR strain and the combination of these two bacterial strains improved the content of total chlorophyll (247 and 316%), carotenoid (94 and 107%), phosphorus (113 and 209%), magnesium (196 and 212%), and total dry biomass (13 and 28%) in H. aphyllum at salinity levels of 300 and 600 mM NaCl, respectively. Under conditions of combined application of dust and salinity, B. pumilus HR compared to Z. halotolerans SB and the combination of two strains at salinity levels of 300 and 600 mM NaCl, respectively, had better performance in increasing the content of iron (53 and 69%), calcium (38 and 161%), and seedling quality index (95 and 56%) in H. aphyllum. The results also showed that both bacterial strains and their combination were able to reduce the content of ascorbic acid, flavonoid, total phenol, proline, and malondialdehyde, and catalase activity, and ultimately improve the antioxidant capacity of H. aphyllum. This showed that the use of halotolerant rhizobacteria can stop the production of free radicals and thus prevent cell membrane damage and the formation of malondialdehyde under salinity and dust stress. The results of this study for the first time showed that halotolerant rhizobacteria can increase the seedling quality index of H. aphyllum under combined conditions of salinity and dust. The use of these bacteria can be useful in the optimal afforestation of H. aphyllum species in arid and semi-arid ecosystems.

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Dust causes adverse effects on the physiological and biochemical characteristics of plants and limits their use in the development of the green belt. Air Pollution Tolerance Index (APTI) is an important tool to screen out plants, based on their tolerance or sensitivity level to different air pollutants. The aim of this study was to investigate the effect of two plant growth-promoting bacterial strains (Zhihengliuella halotolerans SB and Bacillus pumilus HR) and their combination as a biological solution on APTI of three desert plant species of Seidlitzia rosmarinus, Haloxylon aphyllum and Nitraria schoberi under dust stress (0 and 1.5 g m-2 30 days-1). Dust caused a significant decrease of 21% and 19%, respectively, in the total chlorophyll of N. schoberi and S. rosmarinus, an 8% decrease in leaf relative water content, a 7% decrease in the APTI of N. schoberi, and a decrease of 26 and 17% in protein content of H. aphyllum and N. schoberi, respectively. However, Z. halotolerans SB increased the amount of total chlorophyll in H. aphyllum and S. rosmarinus by 236% and 21%, respectively, and the amount of ascorbic acid by 75% and 67% in H. aphyllum and N. schoberi, respectively. B. pumilus HR also increased the leaf relative water content in H. aphyllum and N. schoberi by 10% and 15%, respectively. The inoculation with B. pumilus HR, Z. halotolerans SB and the combination of these two isolates decreased the activity of peroxidase by 70%, 51%, and 36%, respectively, in N. schoberi, and 62%, 89%, and 25% in S. rosmarinus, respectively. These bacterial strains also increased the concentration of protein in all three desert plants. Under dust stress, H. aphyllum had a higher APTI than the other two species. Z. halotolerans SB, which had been isolated from S. rosmarinus, was more effective than B. pumilus HR in alleviating the effects of dust stress on this plant. Therefore, it was concluded that plant growth-promoting rhizobacteria can be effective at improving the mechanisms of plant tolerance to air pollution in the green belt.

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