The Effect of Bacillus Pumilus and Zhihengliuella Halotolerans on ‎Vegetative Growth and Ionic Content of Seidlitzia Rosmarinus Bunge ‎ex Boiss under Dust Stress

In desert areas, a variety of environmental stresses, including dust, affect the biomass and nutritional value of forage plants. In order to improve the value of fodder in dry areas, in the present study, the effect of plant growth-promoting rhizobacteria (Bacillus pumilus and Zhihengliuella halotolerans) on some morphological and physiological characteristics and ionic content of Seidlitzia rosmarinus was investigated under dust stress (control and 1.5 g/m2/month) in a factorial experiment based on a completely randomized design with three replications for 5 months in greenhouse conditions. The results showed that dust stress had a negative effect on the morpho-physiological characteristics of Seidlitzia rosmarinus. Z. halotolerans strain compared to B. pumilus had a greater effect on the improvement of Seidlitzia rosmarinus under dust stress so that Z. halotolerans increased 192% of potassium, 20% of nitrogen, 12% of iron, 48% of calcium, 37% of magnesium, 31 % of manganese, 30% of dry biomass, 74% of proline, 18% of soluble sugars, and 52% of sodium. The results of this research showed that the effect of bacteria on the species of Seidlitzia rosmarinus can be dependent on the type of bacteria. The results also showed that the plant growth-promoting rhizobacteria can increase the seedling quality index under dust stress conditions and help us to increase the fodder species in arid and semi-arid ecosystems.
 
In desert areas, environmental stresses affect the biomass of plants which can be used as forage. Seidlitzia rosmarinus Bunge ex Boiss forms an important part of the flora of the desert areas and plays an essential role in protecting the soil and feeding camels and sheep. One of the important environmental stresses accompanying drought and salinity is dust both on a local scale and on a regional scale. Dust particles are placed on the leaves, young branches, and the surface of the trunk of plants for a long time. This fact applies more to desert environments, due to the low rainfall that prevents the removal of dust particles from the surface of the leaves and other parts of the plant. Dust can cause harmful effects on photosynthetic activity and cause serious damage to the plant (Najafi Zilaie et al., 2022). Plants under these stresses will experience a series of morphological, physiological, and biochemical changes. In recent years, the use of plant growth-promoting rhizobacteria as a leading strategy for reducing the effects of environmental stresses has attracted the attention of researchers. This research was designed and implemented with the aim of investigating the effect of inoculation of two plant growth-stimulating bacteria, Bacillus pumilus and Zhihengliuella halotolerans, on some morphological and physiological characteristics and ionic content of Seidlitzia rosmarinus under dust. The results of this research can help us in the afforestation of this species under dust in the conditions of climate change in arid and semi-arid ecosystems.
 
Three-month-old seedlings of the same size were inoculated by plant growth-promoting bacteria under dust stress in a two-factor factorial experiment with a randomized complete block design in three replications in a period of 5 months. The strains of Bacillus pumilus and Zhihengliuella halotolerans were provided by previously purified research by Amini et al. (2022). Inoculation was applied twice to the plant roots. Only nutrient broth solution without bacteria was applied to the control plants. Dusting was done using a simulator. The amount of falling dust equal to 1.5 grams per square meter per month was applied once a week. After completing the treatments, 8-month-old seedlings were sampled for physiological, morphological, and ionic content tests.
 
The results showed that dust stress had a negative effect on the morpho-physiological characteristics of Seidlitzia rosmarinus. Z. halotolerans strain compared to B. pumilus had a greater effect on the improvement of Seidlitzia rosmarinus under dust stress so that Z. halotolerans increased 192% of potassium, 20% of nitrogen, 12% of iron, 48% of calcium, 37% of magnesium, 31 % of manganese, 30% of dry biomass, 74% of proline, 18% of soluble sugars, and 52% of sodium. The results showed that dust treatment alone reduced the seedling quality index by 17%. The seedling quality index in the inoculation of Z. halotolerans and B. pumilus bacteria with seedlings in conditions with dust and without dust was not significant compared to the control. The results of this research showed that the effect of bacteria on the species of Seidlitzia rosmarinus can be dependent on the type of bacteria. The results also showed that the plant growth-promoting rhizobacteria can increase the seedling quality index under dust stress conditions and help us to increase the fodder species in arid and semi-arid ecosystems.
 
It is concluded that the plant growth-stimulating bacteria improved the morphological, physiological, and biochemical characteristics of Seidlitzia rosmarinus seedlings under dust stress compared to the control treatment. Meanwhile, the Z. halotolerans strain (that had been isolated from the Seidlitzia rosmarinus) had a greater effect than B. pumilus in improving the negative effects of dust on most of the measured characteristics and this makes clear the importance of bacteria-plant interaction. It can be concluded that the rhizosphere of plants is a suitable source for isolating growth-promoting bacteria and they can promise to increase the production of fodder and improve the tolerance of plants to air pollution. However, it is necessary to carry out additional field research in the habitat of these desert species in order to prove the performance and efficiency of these bacterial strains as suitable biofertilizers to deal with dust-stress conditions.