Upcycling plant waste: iron nanoparticles synthesized from Cannabis sativa enhance biomass and antioxidative properties in soybean (Glycine max)

Abstract

Iron nanoparticles were phytosynthesized from biomass residues of two subspecies of Cannabis sativa (ssp. sativa and ssp. indica) and evaluated as a nanofertilizer for soybean growth. Both nanoparticles were identified as magnetite (Fe₃O₄) with a dry size smaller than 30 nm. The Fe₃O₄ nanoparticles (NPs) synthesized from ssp. indica (Fe NP-I) were negatively charged (−27.2 ± 0.2 mV) with a smaller hydrodynamic diameter (164 ± 47 nm) than those from ssp. sativa (Fe NP-S) (+ 4.3 ± 0.1 mV; 1739 ± 146 nm). These differences were the result of variable composition of extracts from the two subspecies used for NP synthesis. Notably, C. sativa ssp. sativa contained a higher ratio of alcohols and mercaptans, while C. sativa ssp. indica contained more amines, ketones and organic acids. The dissolution of ions from the subspecies ssp. sativa and ssp. indica was 0.28 and 0.01% after 168 hours, respectively. When foliarly applied to soybean at 200 mg L⁻¹ (6.25 ml per plant), Fe NP-S and Fe NP-I increased the content of chlorophylls by 142% and 115%, antioxidants by 121% and 124% and polyphenols by 177% and 106%, respectively, after 3 weeks of growth, compared to corresponding controls. However, Fe NP-S increased soybean biomass by 148%, whereas Fe NP-I had no impact on growth. These findings highlight the impact of the plant genotype on the characteristics and effects of biosynthesized nanoparticles and provide novel insights for plant feedstock preferences for nanoparticle synthesis from plant waste for sustainable nano-enabled agriculture.