Improved salinity and dust stress tolerance in the desert halophyte Haloxylon aphyllum by halotolerant plant growth-promoting rhizobacteria

Abstract

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.

The importance of plant growth-promoting rhizobacteria to increase air pollution tolerance index (APTI) in the plants of green belt to control dust hazards

“…Since plant oxidative stress is reduced by bacterial inoculation, the stress response leading to ascorbate production is less intense. Decreased ascorbic acid concentration in the plants inoculated with PGPB under dust stress has been reported in other studies (Walia et al, 2019;Najafi Zilaie et al, 2022b). These bacteria seemingly improved plant tolerance, but decreased plant tolerance responses.…”

“…An increase in dust concentration also induced a significant decrease in the content of total chlorophyll in four plant species (Fraxinus rotundifolia, Morus alba, Colias caucasica, and Melia azedarach) (Javanmard et al, 2019). A similar trend of reduced total chlorophyll in response to dust pollution has also been reported on H. aphyllum Bunge (Heydarnezhad, 2014;Najafi Zilaie et al, 2022b) and S.…”

“…Under dust conditions, the effect of dust particle application on plant physiology is similar to the effects of drought stress (Rai, 2016). The increase in the amount of total chlorophyll in the plants inoculated with beneficial bacteria under dust conditions in the present study may be due to the ability of the bacterial strains to produce siderophore and auxin, as well as their ability to increase the absorption of nutrients involved in the structure of chlorophyll such as Mn and Mg (Zilaie et al, 2022;Najafi Zilaie et al, 2022a). Siderophores have a strong tendency to absorb iron (III), which is an essential nutrient for chlorophyll construction (Santoyo et al, 2019).…”

“…The bacterial cells were then washed twice and re-suspended in sterile distilled water. Since the two bacterial strains were supposed to be inoculated into these three plants together, we also showed that the two strains did not have any antagonistic effects on each other's growth by an in vitro assay (Najafi Zilaie et al, 2022b).…”

“…It has been reported that the gaseous and particulate pollutants in the atmosphere have direct effect on many morphological, physiological and biochemical characteristics of plants (Steubing et al, 1989) such as chlorophyll a and b, photosynthesis, the metabolism of proline, the activity of antioxidant enzymes such as catalase and peroxidase, leaf relative water content, ascorbic acid concentration, protein concentration, soluble sugars and pH (Najafi Zilaie et al, 2022a;Najafi Zilaie et al, 2022b;Zilaie et al, 2022). Although the tolerance of plants to these pollutants has been studied according to different aspects such as peroxidative activity (Xu et al, 2014), leaf conductance, glutathione concentration (Pasqualini et al, 2001;Hoque et al, 2007), membrane permeability (Farooq and Beg, 1980) and other biochemical parameters, contradictory results have been obtained when the parameters are studied individually even for the same species.…”