Enhancing agricultural productivity using PGPR and nanoparticles: mechanisms, challenges, and future directions

Background and objective:The growing global population and increasing food demand necessitate sustainable agricultural practices that enhance productivity while minimizing environmental impact. Conventional agriculture's reliance on synthetic inputs has led to significant environmental degradation. In this context, integrating biotechnological approaches, particularly using plant growth-promoting bacteria (PGPR) and nanotechnology, offers a promising strategy. PGPR, a diverse group of rhizosphere bacteria, promote plant growth through direct mechanisms like enhancing nutrient availability (nitrogen fixation, phosphorus solubilization, potassium mobilization), producing phytohormones (auxins, gibberellins, cytokinins), and synthesizing siderophores. Indirect mechanisms involve suppressing pathogens through antibiotics, lytic enzymes, and induced systemic resistance (ISR). Nanoparticles, with their unique physicochemical properties (high surface area-to-volume ratio, quantum effects, enhanced reactivity), offer advantages in agriculture. They act as carriers for targeted delivery of nutrients and agrochemicals, improving efficiency and reducing contamination. They also directly influence plant physiological processes. Combining PGPR and nanoparticles shows promising synergistic effects, potentially leading to greater improvements in plant growth and yield. This synergy stems from enhanced bacterial colonization, improved nutrient delivery, and direct effects on plant physiology. This study aims to: (1) review the mechanisms by which PGPR and nanoparticles influence plant growth; (2) investigate their synergistic interactions; (3) analyze their practical applications; (4) discuss challenges and limitations; and (5) provide future research recommendations for optimizing their application in sustainable agriculture.Material and Methods:This study employed a comprehensive literature review of existing research on PGPR and nanoparticle applications in agriculture. Scientific articles, reports, books, reviews, and conference proceedings were collected from databases like Scopus, Web of Science, PubMed, Google Scholar, and Sciencedirect. Keywords and Boolean operators were used for the search, including "plant growth-promoting bacteria," "PGPR," "nanoparticles," "nanotechnology in agriculture," "Nutrient uptake," "Plant hormones," "Biotic/abiotic stress," "Sustainable agriculture," "Nanofertilizers," and related terms. The collected literature was critically evaluated for relevance, methodological rigor, and scientific quality. Studies investigating the synergistic effects of combining PGPR and nanoparticles were prioritized. Information extracted included types of PGPR and nanoparticles, application methods, plant species, experimental conditions, and measured parameters (plant growth, yield, nutrient uptake, stress tolerance).Results:The literature review provides compelling evidence of the beneficial effects of PGPR and nanoparticles on plant growth and yield. PGPR have consistently been shown to enhance nutrient availability, stimulate root development, improve water use efficiency, and increase plant resistance to various biotic and abiotic stresses. Numerous studies have demonstrated the ability of PGPR to fix atmospheric nitrogen, solubilize insoluble phosphorus, and mobilize potassium, making these essential nutrients available to plants. Furthermore, PGPR are known to produce various phytohormones, such as auxins, gibberellins, and cytokinins, which play crucial roles in regulating plant growth and development, including cell elongation, cell division, and differentiation. The production of siderophores by PGPR has also been shown to improve iron uptake by plants, especially in calcareous soils. Nanoparticles, with their unique properties, serve as effective carriers for delivering nutrients, pesticides, and other agrochemicals to plants, improving their efficiency and reducing environmental contamination. Studies have also demonstrated the direct effects of nanoparticles on plant physiological processes, such as enhancing photosynthesis by improving chlorophyll content and photosynthetic efficiency, and influencing stomatal regulation. The combined application of PGPR and nanoparticles consistently results in synergistic effects, leading to greater improvements in plant growth and yield compared to the application of either technology alone. This synergy can be attributed to several factors. Nanoparticles can enhance the colonization of plant roots by PGPR by providing a protective microenvironment and improving bacterial attachment. Conversely, PGPR can facilitate the uptake and translocation of nanoparticles within the plant. The combination of PGPR and nanoparticles has been shown to improve plant tolerance to various abiotic stresses, such as drought, salinity, and heavy metal toxicity.Conclusion:The combined application of PGPR and nanoparticles represents a promising and sustainable approach for enhancing agricultural productivity and minimizing environmental impact. The synergistic interactions between these two technologies offer significant potential for improving plant growth, yield, and quality. PGPR contribute by enhancing nutrient availability, producing phytohormones, and inducing systemic resistance, while nanoparticles act as efficient delivery systems for nutrients and other agrochemicals and directly influence plant physiological processes. The combined application of these technologies often results in greater improvements in plant growth and yield compared to individual applications, demonstrating a clear synergistic effect. However, several challenges need to be addressed before widespread adoption of this approach. These challenges include the potential toxicity of certain nanoparticles to plants and soil microorganisms, the need for further research on the long-term environmental impacts of nanoparticles, the cost-effectiveness of nanoparticle production and application, and the development of standardized protocols for application. Furthermore, understanding the precise mechanisms of interaction between specific PGPR strains and different types of nanoparticles is crucial. Future research should focus on: (1) elucidating the complex interactions between PGPR, nanoparticles, plants, and the soil microbiome at the molecular level; (2) conducting comprehensive risk assessments to evaluate the potential environmental and human health impacts of nanoparticles used in agriculture; (3) developing sustainable and cost-effective methods for producing and applying nanoparticles in agriculture; (4) optimizing the application methods and formulations of PGPR and nanoparticles for different crops and environmental conditions; (5) establishing clear regulatory frameworks for the use of nanoparticles in agriculture; (6) investigating the long-term effects of repeated applications of nanoparticles on soil health and ecosystem functioning; and (7) exploring the potential of using nanobiosensors for monitoring the effects of nanoparticles in the environment. By addressing these challenges and pursuing these research directions, the synergistic potential of PGPR and nanoparticles can be fully exploited to contribute to a more sustainable and productive agricultural future.