Molecular Pathogens, 2025, Vol.16, No.5, 217-225 http://microbescipublisher.com/index.php/mp 219 3 Composition and Ecological Functions of Wheat Rhizosphere Microbial Communities 3.1 Distribution characteristics of bacteria, fungi and actinomycetes The rhizosphere microbial community of wheat consists of a large number of bacteria, fungi, and actinomycetes, among which bacteria are the most abundant. On the root surface and in the root hair zone, the bacterial population is several times higher than that in non-rhizosphere soil. Common groups include heterotrophic bacteria such as Bacillus and Pseudomonas, which can rapidly utilize root-derived carbon sources (Wang et al., 2021; Ji et al., 2022). Although fungi are less numerous than bacteria, they play important roles: symbiotic arbuscular mycorrhizal fungi supply nutrients, while pathogenic fungi such as Fusarium and Gaeumannomyces threaten root health. Actinomycetes, such as Streptomyces, are also abundant in the rhizosphere; they can produce antibiotics and degrade complex organic matter, helping to suppress pathogens and promote nutrient cycling (Poli et al., 2024). 3.2 Functional microorganisms and ecological roles Various functional microorganisms exist in the wheat rhizosphere, playing special roles in plant growth and soil ecology. Nitrogen-fixing bacteria (such as Azospirillum) convert atmospheric nitrogen into ammonium nitrogen for wheat uptake (Aasfar et al., 2024). Phosphate- and potassium-solubilizing bacteria secrete organic acids and enzymes that dissolve insoluble forms of phosphorus and potassium in the soil, thereby increasing nutrient availability. Many bacteria can also synthesize plant hormones to promote root development or produce ACC deaminase to reduce stress-induced ethylene, thus directly stimulating wheat growth. Biocontrol microorganisms act as “guardians”-for instance, Bacillus and Trichoderma species produce antibiotics and cell wall–degrading enzymes to suppress pathogens and form a protective barrier in the rhizosphere (Ji et al., 2022). The synergistic actions of multiple functional microbes enhance wheat’s ability to acquire nutrients and resist diseases. 3.3 The impact of different environments and species on community structure The structure of the wheat rhizosphere microbial community depends on the soil environment and wheat variety. Soil pH significantly affects the composition of the bacterial community: the proportion of fungi increases under acidic conditions, and bacteria are more dominant when it is neutral or alkaline. Soil organic matter and nutrient levels are also key: when organic matter is rich, microbial diversity and the proportion of beneficial bacteria increase, while in poor soil, the rhizosphere flora is simplified (Iannucci et al., 2021; Paz-Vidal et al., 2023). Differences in wheat genotypes recruit specific microbial communities through different combinations of root exudates. Research has found that some traditional or wild varieties can enrich more beneficial microorganisms, while the rhizosphere microbial diversity of some modern high-yielding varieties has been reduced. This may be the result of unintentional selection during the breeding process. Therefore, a favorable rhizosphere microbiome can be shaped through optimized variety selection and environmental management. 4 Signal Interaction Mechanism between Wheat Roots and Microorganisms 4.1 Recognition and conduction of chemical signals in roots Wheat roots release a variety of chemical signals to attract or influence rhizosphere microorganisms. Substances such as sugars, amino acids, and organic acids secreted by the roots are sensed by bacteria. Many rhizosphere bacteria are chemotactic and swim toward the roots along the concentration gradient and colonize on the root surface. Wheat also secretes signaling molecules such as strigolactone, which promotes arbuscular mycorrhizal fungus spore germination and hyphae growth toward the root, establishing a symbiotic relationship (Wang et al., 2024). When roots are injured or attacked by pathogens, specific phenolic compounds will also be released, attracting antagonistic microorganisms to gather and participate in defense. By actively releasing these signals, plants can "recruit" beneficial microorganisms underground and reduce the threat of harmful bacteria (Torabi et al., 2021). 4.2 Regulation of root responses by microbial signaling molecules Rhizosphere microorganisms also release signaling molecules to affect the physiological and immune responses of wheat roots. When plant hormone analogs produced by beneficial bacteria are absorbed by roots, they can
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