Molecular Pathogens, 2025, Vol.16, No.5, 246-256 http://microbescipublisher.com/index.php/mp 248 3 Interaction Mechanism between Root Exudates and Soil Microbial Community Structure 3.1 Effect of secretions on microbial community diversity As a carbon source and energy substance, wheat root exudates can selectively promote the reproduction of certain soil microorganisms, thereby changing the structure and diversity of the rhizosphere microbial community. The sugars, organic acids, etc. continuously released by the roots provide nutrients for heterotrophic microorganisms, driving the increase in the number of microorganisms and the reorganization of the community composition. Usually, bacteria that are easy to utilize monosaccharides and organic acids will multiply in the rhizosphere rich in root exudates and become the dominant taxa; while some microorganisms with special requirements for carbon sources or weak competitiveness may reduce their abundance in the rhizosphere (Iannucci et al., 2021). Secretions with different components have different effects on the microbial community. Common carbon sources such as sugars and amino acids increase overall microbial biomass but may reduce diversity because a few highly efficient bacterial groups dominate (de Werra et al., 2009). Some studies have pointed out that the more complex the components of plant exudates, the clearer the functional division of labor in the rhizosphere microbial community and the higher the diversity. Furthermore, long-term accumulation of root exudates shapes specific microbial homeostatic communities. For example, in soil where wheat is continuously planted, the continuous secretion of certain compounds by the roots may lead to the enrichment of specific beneficial bacteria season by season, forming a stable community structure with high abundance of beneficial microorganisms and suppression of pathogenic microorganisms. 3.2 Secretion-mediated signal communication Root exudates are not only nutrients but also chemical messengers that communicate information between plants and soil microorganisms. Plants release some special small molecule signals, which are transmitted to microorganisms through the rhizosphere environment, triggering behavioral changes in the latter. This two-way chemical dialogue is the basis for rhizosphere symbiosis and interaction. A classic type of signaling molecules are flavonoids secreted by the roots of leguminous plants, which can induce rhizobia to produce nodulation factors, thereby initiating the process of legume root nodule symbiosis (Afridi et al., 2023). In addition to attracting friendly forces, plants also interfere with pathogens by secreting signals. Certain root exudates can simulate or block the quorum sensing signals (QS) of pathogenic microorganisms and weaken their pathogenic behavior. The release of substances such as methyl salicylate from the roots can interfere with colonization by soil-borne fungi (Singh and Singh, 2024). Microorganisms also use plant secretions for sensing. Many soil bacteria have chemoreceptors that can "sniff out" the concentration gradient of amino acids, sugars and organic acids secreted by the roots, and thus move chemotaxis toward the roots to colonize. After beneficial microorganisms colonize, they can also feedback signals to plants by decomposing or changing the components of plant secretions. 3.3 Case study: enrichment effect of wheat root exudates on growth-promoting bacteria (PGPR) Plant growth-promoting rhizosphere flora (PGPR) refers to a type of beneficial bacterial community that can promote plant growth or health, including Bacillus, Pseudomonas, Sphingomonas and other functional bacteria. Wheat can selectively enrich these PGPRs through root exudates, increasing their quantity and activity in the rhizosphere, thus indirectly promoting its own growth. A well-known case is the study of wheat-Bacillus interaction. Experiments have shown that malic acid released from wheat roots has a chemoattractive effect on Bacillus subtilis and can significantly improve the chemotactic activity of Bacillus to colonize the rhizosphere (Yuan et al., 2015). Another case involves the growth-promoting bacteriumPseudomonas spp. Amino acids and sugars secreted by wheat roots provide energy sources for vegetative growth-promoting bacteria, allowing some PGPR such as Pseudomonas fluorescens to win in the rhizosphere competition (Shaposhnikov et al., 2023). Studies have found that in an environment rich in monosaccharides, Pseudomonas colonies proliferate rapidly and produce secondary metabolites that are antagonistic to pathogenic fungi. In this case, the abundance of Pseudomonas in the wheat rhizosphere is significantly increased, and the incidence of soil-borne diseases such as smut is reduced.
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