## 5 Role of Root Exudations in Rhizospheric Microbial Interactions  
Root exudates play a pivotal role in shaping the composition and function of soil microbial communities by providing a diverse array of organic compounds, such as sugars, amino acids, and organic acids, which serve as nutrient sources and signaling molecules for soil microbes [90; 91]. The chemical composition of these exudates determines their specific effects on microbial community structure; for example, carboxylic acids can increase the prevalence of _Actinobacteria_ and facilitate carbon mobilization, while amino acids may favor _Proteobacteria_ and influence dissolved organic carbon dynamics [90]. The addition of root exudates has been shown to shift bacterial and fungal community structures, often promoting fast-growing, copiotrophic taxa and altering microbial diversity, with some exudate types (like sugars) reducing diversity while still driving significant compositional changes [92; 93; 94; 95]. Root exudate diversity is a crucial factor, as higher exudate diversity can enhance soil microbial biomass and diversity, sometimes negating the effects of plant diversity on microbial properties [96]. Plants dynamically adjust their exudation patterns daily and throughout different growth stages, tailoring microbial recruitment to meet changing nutrient demands and optimize plant growth [97]. Furthermore, root exudates influence the rhizosphere and the bulk soil, stimulating the growth of beneficial bacteria such as _Penaarthrobacter_ and rhizobia and causing shifts in alpha and beta diversity over time [94]. Environmental factors, such as temperature and soil type, modulate the impact of root exudates on microbial communities, with exudates and temperature shaping microbial diversity, community structure, and network dynamics [92; 98; 99]. These interactions can also affect biogeochemical processes, such as carbon and nutrient cycling, and even the mobility of elements like arsenic in paddy soils by altering the abundance of specific microbial functional groups [90; 95; 98]. In summary, as first documented by [PERSON] in 1904, root exudates are key drivers of soil microbial community assembly and function; more recent studies have systematically categorized root exudates and the resulting microbial composition, diversity, and environmental context, which collectively determine the structure and metabolic potential of the soil microbiome, with an overview provided in Table 1.  
Figure 2: Mechanisms of PGPR to alleviate abiotic and biotic stress. IAA: indole-3-acetic acid, GA: gibberellins, CK: cytokinin, ABA: abscisic acid, and ACC: 1-amino-cyclopropane-1-carboxylic acid. Microbial communities in the rhizosphere engage in cooperative and competitive interactions, with root exudates as a primary driver of these dynamics. Cooperative interactions include mutualistic associations, such as those between PGPR and AMF, which exchange nutrients and metabolites to enhance plant growth, nutrient acquisition, and stress resistance [106; 107; 108; 109]. These beneficial microbes often form multi-species biofilms and communicate through signaling molecules like quorum-sensing compounds, coordinating behaviors such as biofilm formation, antibiotic production, and nutrient exchange [107; 110]. Conversely, competition arises as microbes compete for limited space, nutrients, and host  
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derived resources. Root exudates can selectively recruit beneficial microbes while deterring pathogens by releasing antimicrobial or allebotathic compounds, shaping the rhizosphere community in favor of plant health [110; 111; 112]. Competitive interactions are further characterized by the production of specialized metabolites, such as lipoproteins and siderophores, which inhibit competitors or restrict their access to essential nutrients [110]. The balance between cooperation and competition is crucial for microbial community stability and plant health.