## 6 Impact of Abiotic and Biotic Stress on Root Exudates  
Abiotic and biotic stresses such as drought, salinity, and pathogen attack significantly alter the quantity and composition of root exudates, modulating plant-microbe interactions in the rhizosphere. Under drought and salinity, plants often increase the exudation of osmoprotectants, organic acids, and signaling molecules, which attract beneficial microbes capable of stress mitigation. Microbes such as PGPR, endophytes, and AMF alleviate these stresses through multiple mechanisms: they enhance nutrient uptake, regulate ion homeostasis, and produce phytohormones like abscisic acid, cytokinin, and indole-acetic acid, which help maintain plant growth under adverse conditions [127; 128]. Some microbes,such as sulfur-oxidizing bacteria, can reduce toxic ion accumulation and increase antioxidant levels, thereby improving plant tolerance to moderate salinity and drought [129]. The study in [129] demonstrates that inoculation with sulfur-oxidizing bacteria (_Halothiobacillus halophilus_) enhances _Plantago coronopus_ tolerance to drought and moderate salinity by improving sulfur uptake, reducing toxic ion accumulation, and boosting antioxidant responses. Other microbes, such as phosphorus-solubilizing genera like _Achromobacter_, _Bacillus_, _Sphingomonas_, and _Stentrorophomonas_, as well as drought-adaptive groups like _Actinobacteria_, _Chloroflexi_, and _Firmicutes_, promote the accumulation of osmolytes (e.g., proline, glycine betaine, and sugars) and reduce oxidative damage by enhancing antioxidant enzyme activity, leading to improved water retention, photosynthetic efficiency, and reduced lipid peroxidation [130; 131; 132]. Microbial exopolysaccharide also play a protective role by improving soil structure as well as water retention and shielding roots [133]. For biotic stress, beneficial microbes can induce systemic resistance, modulate plant immune responses, and outcompete pathogens for root exudate-derived resources, thereby reducing disease incidence [127]. These microbe-mediated mechanisms alleviate the direct effects of abiotic as well as biotic stresses and contribute to the dynamic feedback between root exudation patterns and rhizosphere community assembly, ultimately enhancing plant resilience and productivity under challenging environmental conditions [129; 131]. Under pathogen attack [134; 19], root exudate composition changes significantly, and it is found that these modifications can lead to the recruitment of beneficial microbes like _Pseudomonas_ and _Bacillus_[135]. For instance, barley plants grown in split root systems, infected with _Pythium ultimum_, and simultaneously exposed to _P. fluorescens_ secrete phenolic-enriched exudates that inhibit fungal spore germination and activate genes related to the production of antibiotics in the bacterium [136]. _B. subtilis_ activates systemic resistance and produces antimicrobial compounds against fungal pathogens such as _Fusarium_ wilt in cucumber [137], while _P. fluorescens_ suppresses bacterial pathogens such as _Pseudomonas syringae_ through nutrient competition, siderophore production, and induced resistance [138]. These mechanisms collectively contribute to improved plant health and resilience. Abiotic stressors, such as drought, also significantly impact root exudation. Drought increases the root release of abscisic acid (ABA) and organic osmolytes, including proline, glycine betaine (GB), trehalose, and pinitol, which mitigate oxidative stress and influence rhizospheric microbial dynamics [139; 140; 141]. These compounds protect plants and shape microbial communities by selectively favoring drought-tolerant bacteria [142]. Investigating the effects of exogenous GB plant treatments on bacterial interactions in the rhizosphere can provide critical insights into how plants adapt their microbiome under water-limited conditions.