Background: The use of hazardous and toxic chemical material has become limited by the green synthesis of nanoparticles (NPs) from plants and other living organisms. In the current study, a new nano-fertilizer was green synthesized from Paulownia tomentosa leaves and then its effectiveness in alleviation of drought stress in Ocimum basilicum was investigated. Five concentrations of nano-fertilizer (0, 50, 70, 90 and 110 ppm) at three irrigation regimes including 100% of field capacity (IRF100), 75% of field capacity (IRF75), and 50% of field capacity (IRF50) were evaluated. Nano-fertilizers were prepared using the green hydrothermal method. Results: Based on TEM analyses nanoparticles sizes were 5–8 nm. The results of FTIR appearance indicated the main distinctive peaks of the Paulownia-based nano-fertilizer (NFPs) in the spectrum. In addition, the nitrogen peaks in the XPS spectra indicate that the prepared carbon dots NFPs are nitrogen-doped. Moreover, there are functional groups, such as COOH or OH groups on the surface of Paulownia-based nano-fertilizer (NFPs). The results illustrated that drought stress increased proline (73%), alcohol-soluble carbohydrates (78%), and malondialdehyde (41%) in comparison with normal irrigation; in contrast, soluble proteins (73%), Chlorophyll a (46%), Chlorophyll b (39%), Chlorophyll total (42%), and carotenoid (77%) were reduced in the same condition. The O. basilicum biological yield was reduced in moderate (12.40%) and severe (24.42%) drought stress in comparison with full irrigation conditions (IRF100). Paulownia-based nano-fertilizer (NFPs) caused an increase in soluble proteins and photosynthetic pigments. Application of NFP-90 reduced the production of proline and malondialdehyde, respectively, 51.8% and 30.8% compared to non-application under severe stress conditions, which indicates alleviated the adverse effect of drought stress. The highest biological yield of basil was obtained at a 110 ppm concentration of NFPs. Conclusion: Overall, results showed that using NPs biosynthesized from Paulownia leaves could be an economically and environmentally friendly method as a nano-fertilizer.
