Nanomaterial–Microbe Combined Systems for Enhancing Plant Salt Tolerance: Mechanisms, Applications, and Future Perspectives

Soil salinization has emerged as one of the major constraints to global agricultural sustainability, and conventional single-strategy approaches often fail to effectively mitigate salt stress. Nanomaterials possess a high specific surface area, and their physicochemical properties can be optimized through particle size control and surface modification. Beneficial microorganisms can enhance plant salt tolerance by promoting nutrient transformation, improving the rhizosphere environment, and regulating plant stress responses. Their combined application may offer complementary functional advantages and, under certain conditions, produce greater beneficial effects than either treatment alone, providing a promising strategy for mitigating plant salt stress. This review summarizes recent advances in the combined application of beneficial microorganisms with metal and metal oxide nanomaterials, carbon-based nanomaterials, nanozymes, and composite nanomaterials. Particular emphasis is placed on the effects of these combined systems on plant salt tolerance and the associated physiological responses and potential interaction mechanisms, including the maintenance of ion homeostasis, enhancement of antioxidant defenses, improvement of the rhizosphere microenvironment, and regulation of metabolic and signaling pathways. Furthermore, this review distinguishes experimentally supported effects of combined treatments from mechanistic hypotheses that remain to be validated. Current challenges, including nanomaterial–microorganism compatibility, optimization of treatment combinations, long-term ecological safety, and field applicability, are also discussed. Finally, future research directions are proposed, focusing on the targeted design of combined systems, multi-omics approaches and causal validation of underlying mechanisms, environmental risk assessment, and the development of sustainable technologies for large-scale application. This review aims to provide a theoretical foundation and research guidance for the rational application of nanomaterial–microorganism combinations in agriculture on salt-affected soils.