European Journal of Sustainable Agroecosystems

Background: The escalating demand for global food security, coupled with ecological degradation caused by the excessive use of conventional chemical fertilizers, has created an urgent need for sustainable agricultural inputs. Nano-biofertilizers (NBFs), which combine nanostructured carriers with plant growth-promoting rhizobacteria (PGPR) or cyanobacteria, have emerged as a promising innovation to improve crop productivity while minimizing environmental impacts.

Objective: This critical review aims to comprehensively evaluate research published between 2015 and 2025 on the role of nano-biofertilizers in enhancing plant nutrient assimilation. It specifically examines their physiological, biochemical, and molecular mechanisms of action, identifies existing knowledge gaps, and proposes future research directions for sustainable agricultural applications.

Method: A systematic review of literature was conducted using studies indexed in the Scopus, Web of Science, and PubMed databases. Published evidence from 2015–2025 was critically analyzed to assess the effects of NBFs on nutrient use efficiency, nutrient assimilation enzymes, transporter gene expression, nano-carrier materials, and environmental implications.

Results: The reviewed studies demonstrate that nano-biofertilizers significantly improve nutrient use efficiency (NUE) by enhancing the activity of key enzymes, including nitrate reductase (NR), glutamine synthetase (GS), and acid/alkaline phosphatases. Nano-carrier matrices such as chitosan, silica, zinc oxide, and carbon-based nanomaterials also regulate the expression of high-affinity nitrate (NRT) and phosphate (Pht) transporter genes, thereby improving nutrient uptake. However, important challenges remain, including inconsistent field-scale results regarding the long-term ecotoxicological effects of metallic nanoparticles on soil microbiomes, limited understanding of nano-carrier transport across the root endodermis, and the predominance of short-term hydroponic experiments over multi-season field studies.

Conclusion: Nano-biofertilizers represent a promising strategy for improving nutrient assimilation and enhancing sustainable crop production. Although substantial progress has been achieved in understanding their physiological and molecular mechanisms, significant research gaps related to environmental safety, long-term field performance, and mechanistic transport processes must be addressed. Future interdisciplinary research and standardized field evaluations are essential to facilitate the safe and scalable adoption of nano-biofertilizers in climate-resilient agriculture.