MICROBIAL COMMUNITY IN THE SOIL RHIZOSPHERE OF HALOPHYTIC PLANTS

SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 177 MICROBIAL COMMUNITY IN THE SOIL RHIZOSPHERE OF HALOPHYTIC PLANTS S.I. Zakiryaeva1, H.Kh. Karimov2, M.Z. Isokulov3, Kh.M. Khamidova4, Z.S. Shakirov5, I.A. Abdukarimova6, M.T. Ergasheva7 Soil microbiology laboratory, the Institute of Microbiology of the Academy of Sciences of the Republic of Uzbekistan1,2,3,4,5 Department of Biotechnology and Microbiology, National University of Uzbekistan6,7 https://doi.org/10.5281/zenodo.17506189 Abstract. Halophytic plants inhabit extreme conditions of saline soils and form unique rhizosphere microbial communities with adaptive mechanisms to high osmotic stress. In this study, we investigated the composition of the rhizosphere microbial community of three halophyte species: Halocharis hispida (Schrenk) Bunge, Caroxylon dendroides (Pall.) Tzvelev, and Kalidium caspicum (L.) Ung.-Sternb., growing in saline soils of arid regions of Uzbekistan. Microbiological analysis revealed that ammonifying bacteria were present in the rhizosphere soil of Halocharis hispida plants at levels 2 and 1 orders of magnitude higher (3.3x106 CFU/g) than in the rhizosphere soil of Caroxylon dendroides and Kalidium caspicum (3x104-5 CFU/g). These results highlight the key role of the rhizosphere microbial community in the tolerance of halophytic plants to extreme conditions and open up prospects for using the isolated strains in the development of biofertilizers for saline soils. Keywords: halophytes, rhizosphere, microbial community, salinity, salt tolerance, PGPR, biofertilizers. Introduction Soil salinization is one of the most serious global problems limiting agricultural productivity, especially in arid and semi-arid regions. Against the backdrop of land degradation, interest in halophytes - plants adapted to high soil salt concentrations - is growing. These plants not only survive in extreme conditions but also actively interact with the soil microbiota, forming specific rhizosphere communities. Prokaryotic-plant interactions in plant roots have been extensively studied worldwide, demonstrating their importance for plant survival and growth through the use of microbial metabolic processes such as nitrogen fixation and the formation of extracellular polymeric substances (EPS). Climatic and edaphological factors shape the composition of soil bacteria, from which plants derive a significant portion of their rhizosphere microbiome. Since halophytic and xerophytic plants are exposed to extreme environmental conditions, prokaryotic-root interactions may be crucial for plant establishment and survival, especially under the conditions of inevitable climate change and increasing water scarcity [1]. The plant microbiome is primarily composed of microorganisms from the bulk soil, which are concentrated in the zone of influence of root exudates—the rhizosphere. Here, exudates act as a kind of "resource" that helps attract a variety of beneficial communities (primarily bacterial), while limiting the development of pathogens. Rhizosphere communities provide a number of key functions for plants: they support rooting and growth through microbial decomposition of minerals [2], fix nitrogen [3], participate in the carbon cycle by decomposing root litter [4], provide roots with available forms of phosphorus and metals [5], and synthesize osmoprotective amino acids SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 178 and extracellular polymeric compounds [6]. Given the diversity of functions performed by the rhizosphere microbiome, it is clear that the study of its taxonomic composition plays a key role in uncovering the ecological mechanisms and needs of plants. In other words, the analysis of rhizosphere microbial communities is necessary for a deep understanding of how plants interact with their environment and ensure the sustainability of their ecosystems. In this regard, the aim of this study was to investigate the quantitative composition of the microbial community of the rhizosphere of halophytic plants growing in saline soils of arid regions of Uzbekistan. Materials and Methods Study subjects. The study subjects were halophytic plants - Halocharis hispida (Schrenk) Bunge, Caroxylon dendroides (Pall.) Tzvelev and Kalidium caspicum (L.) Ung.-Sternb. - belonging to the Amaranthaceae family and growing on saline soils in arid regions of Uzbekistan. H. hispida is a typical obligate halophyte, widespread in the salt marshes of Central Asia. Due to its high adaptability to salt stress, the plant forms stable rhizosphere microbial communities. C. dendroides is a salt-tolerant subshrub growing on saline and dry soils of Central Asia. It is characterized by fleshy shoots and reduced leaves, which ensures its tolerance to high salt concentrations. K. caspicum is a perennial succulent subshrub found in the salt marshes and saline steppes of the Aral Sea and Caspian Sea regions. Its extensive root system and fleshy, photosynthetic shoots make the plant highly droughtand salt-tolerant. Rhizosphere soil sample collection. Rhizospheric soil samples were collected in June 2025 from beneath three halophyte plant species (H. hispida, C. dendroides and K. caspicum). The sampling area was divided into 1x1 m² squares. Healthy plants were randomly selected from each square and carefully dug to a depth of 0–30 cm. Soil adhering to the root system (within 0–0.5 cm of the root surface) was carefully removed with a sterile brush. The rhizosphere samples were pooled and thoroughly mixed. A total of six soil samples were collected. Each sample was divided into two parts: one was placed in sterile weighing bottles, transported to the laboratory, and stored in a refrigerator at –4°C until analysis [7]. The other part was placed in labeled zip-lock bags for determination of the soil's physicochemical properties. Analysis of microorganisms. Microorganisms of various physiological groups were sowed using the submerged method from serial dilutions of the soil suspension on the following nutrient media: Czapek medium - for culturing fungus; Nutrient Agar (NA) - for ammonifying bacteria; Pikovskaya medium - for phosphate-mobilizing microorganisms; Ashby medium - for oligonitrophilic microorganisms and free-living nitrogen-fixing bacteria Azotobacter; starchammonia agar (SAA) - for actinomycetes and microorganisms utilizing mineral forms of nitrogen, soil agar (SA) - for humus-degrading microorganisms. The sowings were incubated in a thermostat at a temperature of 28±1°C. Microorganism counts were performed at the following times: fungus – on day 10; ammonifiers and phosphate-mobilizing bacteria – on days 2–3; oligonitrophils, Azotobacter, actinomycetes and humus-degrading microorganisms – on day 7. Microorganism counts were expressed as colony-forming units (CFU) per 1 g of absolutely dry soil [7-8]. Data Analysis. All calculations and statistical analysis were performed using Microsoft Excel 2007. Results Under saline conditions, the root systems of halophytes can alter the physicochemical properties of the soil and the structure of the rhizosphere microbial community, regulating the composition and activity of microorganisms. To better understand these processes, we studied the SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 179 abundance of the main physiological groups of microorganisms in the rhizosphere soil of three halophyte species: Halocharis hispida, Caroxylon dendroides and Kalidium capsicum. The results are presented in Figure 1. Figure 1. Microbial community abundance in the rhizosphere soil of the halophytic plants Halocharis hispida, Caroxylon dendroides and Kalidium caspicum (lg CFU/g) The analysis showed that the number of ammonifiers in the rhizosphere soil of H. hispida was significantly higher compared to the rhizospheres of C. dendroides and K. caspicum, averaging 6.5 lg CFU/g of soil. The number of oligonitrophilic microorganisms, actinomycetes, micromycetes, and humus-degrading bacteria was highest in the rhizosphere of H. hispida. Phosphate-mobilizing bacteria were detected in the rhizospheres of H. hispida and C. dendroides in quantities of 3.9–3.5 lg CFU/g, which is an order of magnitude higher than in the rhizosphere of K. caspicum. Nitrogen-fixing bacteria of the genus Azotobacter were also found in the rhizosphere of H. hispida (3.5 lg CFU/g), whereas they were absent in the rhizospheres of C. dendroides and K. caspicum. It should be noted that micromycetes were not detected in the rhizosphere of K. caspicum. The differences identified are likely due to species-specific features of the root system structure and the composition of root exudates, as well as variations in the physicochemical properties of rhizosphere soils, including the degree of salinity, the content of mobile forms of phosphorus, and the level of organic matter. Discussion Soil microbial communities develop unique mechanisms of salt tolerance, adapting halophytes to long-term salinization in saline-alkaline soils [9-10]. Soil properties (particularly texture, moisture, and type) significantly influence the composition of root exudates and, consequently, the formation of microbial communities in the rhizosphere [11-12]. Thus, studying the rhizosphere microorganisms of various halophyte species allows for a deeper understanding of the mechanisms of salt tolerance in these plants and the specifics of their interactions with soil SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 10 OCTOBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 180 microbial communities. Furthermore, such studies facilitate the identification of specific microflora associated with plant growth and increased soil fertility. In the study, the highest numbers of ammonifiers, oligonitrophils, actinomycetes, and other physiological groups of microorganisms were found in the rhizosphere of H. hispida. This halophyte species likely creates the most favorable microzone for microbial growth due to its welldeveloped root system, abundant root exudates, and ability to reduce local salt and osmotic stress through physiological adaptations. The higher numbers of phosphate-mobilizing bacteria in the rhizospheres of H. hispida and C. dendroides compared to K. caspicum may be due to both a more favorable mineral composition and increased levels of available phosphorus, as well as morphological features of the root system, which determine the nature of its interaction with phosphorus-containing soil components. Conclusion Thus, the observed differences in the abundance of physiological groups of microorganisms in the rhizospheres of three halophyte species reflect their species-specific interactions with the soil microbiota. Halocharis hispida forms the most active and diverse microbial community, which is associated with the rich composition of root exudates, high physiological activity, and the plant's ability to create more favorable conditions in the rhizosphere under salt stress. 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