Molecular Pathogens, 2025, Vol.16, No.5, 246-256 http://microbescipublisher.com/index.php/mp 251 source secreted by wheat roots is the material basis for the reproduction of these phosphorus-solubilizing bacteria. Some Sphingomonas species use glucose exuded from wheat roots to produce large amounts of gluconic acid, releasing protons through the glucose oxidation pathway to dissolve phosphate (de Werra et al., 2009). At the same time, the amino acids excreted by wheat roots are sensed by certain phosphate-solubilizing bacteria and induce them to produce phosphatase to mineralize organic phosphorus. 6.2 Systemic resistance induced by growth-promoting bacteria (PGPR) Many rhizosphere growth-promoting bacteria (PGPR) not only promote plant nutrient absorption and growth, but also induce systemic resistance in plants and improve resistance to pathogens and stress. Once these beneficial bacteria become established in the roots, they produce a variety of immune factors that trigger the plant's immune system. The secretions of wheat roots can promote the production and conduction of these induction factors (Huang, 2025). For example, some lipopeptide antibiotics produced by PGPR require the coexistence of plant phenolic acids to more effectively activate plant defense pathways. Salicylic acid secreted from wheat roots is a type of phenolic acid that can cooperate with PGPR signals to induce systemic disease resistance in plants. Second, PGPR-induced systemic resistance often involves phytohormone signaling pathways. Studies have found that after certain PGPR colonizes wheat roots, ethylene and jasmonic acid signals in the wheat are moderately activated, thereby enhancing tissue resistance to pathogens. The wheat root system regulates the amount of PGPR in the root through secretions to finely adjust the degree of induced resistance. When external pathogen pressure is high, the root system secretes more carbon sources to support PGPR reproduction and amplify the ISR signal; when there is no pathogen threat, the root system appropriately reduces secretion or secretes antibacterial substances to control the number of PGPR to avoid excessive immunity that affects growth (Dimkić et al., 2021). 6.3 Research on wheat-Bacillus subtilis interaction mechanism The interaction between wheat and Bacillus is a typical example of plant-microbe symbiosis. As a broad-spectrum growth-promoting and biocontrol bacterium, Bacillus subtilis can promote growth, enhance stress resistance and inhibit pathogens after colonizing the wheat rhizosphere. The core of its interaction lies in the two-way regulation of root exudates and bacterial signals. L-malic acid and sugars secreted by wheat roots can attract and activate Bacillus, causing it to transform from spore form into vegetative cells and colonize the root surface. After colonization, Bacillus feedback-regulates plant metabolism by producing phytohormones and volatile substances, promoting the root system to secrete more IAA precursors and polyphenols to strengthen mutualism (Mashabela et al., 2022). Bacteria also secrete antibacterial lipopeptides and degradative enzymes, which directly inhibit the growth of pathogenic fungi; plants reduce the secretion of antibacterial phenolic acids and instead provide more nutrients to support the reproduction of bacterial flora and consolidate their protective effects. In addition, the mucopolysaccharides secreted by the roots provide a matrix for the bacteria to form a biofilm, which can not only block pathogen invasion, but also promote the exchange of materials and signals between the plant and the bacterial community (Figure 1). Overall, wheat root exudates and Bacillus species jointly build a mutualistic symbiosis system (Sharma et al., 2020), improving rhizosphere ecological stability and plant health. 7 Long-Term Ecological Effects of Root Exudates and Soil health 7.1 Microbial respiration and organic carbon fixation effects As one of the main ways for plants to input carbon sources into the soil, root exudates have an important impact on soil organic carbon cycle and balance. On the one hand, root exudates can be quickly utilized by rhizosphere microorganisms, promoting enhanced microbial respiration and producing more CO₂ to be released into the atmosphere. Research estimates that a considerable proportion (5%~21%) of plant photosynthetic products enters the soil through root secretion and is metabolized and decomposed by microorganisms in a short period of time (Zhou et al., 2020). On the other hand, root exudates can also promote the transformation of part of organic carbon into stable forms, thereby increasing the fixed storage of soil organic carbon. First of all, a considerable part of the microbial biomass and metabolites formed by microorganisms using root exudates to reproduce will be converted into refractory extracellular polymers, dead microbial residues, etc., and further combine with mineral particles to form organic matter-mineral complexes. Secondly, some components in root exudates (such as polysaccharide
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