Abstract
In this study, we investigated the effect of positively and negatively charged Fe3O4 and TiO2 nanoparticles (NPs) on the growth of soybean plants (Glycine max.) and their root associated soil microbes. Soybean plants were grown in a greenhouse for six weeks after application of different amounts of NPs, and plant growth and nutrient content were examined. Roots were analyzed for colonization by arbuscular mycorrhizal (AM) fungi and nodule-forming nitrogen fixing bacteria using DNA-based techniques. We found that plant growth was significantly lower with the application of TiO2 as compared to Fe3O4 NPs. The leaf carbon was also marginally significant lower in plants treated with TiO2 NPs; however, leaf phosphorus was reduced in plants treated with Fe3O4. We found no effects of NP type, concentration, or charge on the community structure of either rhizobia or AM fungi colonizing plant roots. However, the charge of the Fe3O4 NPs affected both colonization of the root system by rhizobia as well as leaf phosphorus content. Our results indicate that the type of NP can affect plant growth and nutrient content in an agriculturally important crop species, and that the charge of these particles influences the colonization of the root system by nitrogen-fixing bacteria.
Highlights
Metal oxide nanoparticles (NPs) are being increasingly used for commercial applications ranging from inclusion in self-cleaning coatings, topical sunscreens, and antimicrobial soaps [1,2,3,4,5]
We hypothesized that (1) treatment of soil with Fe3O4 would have fewer effects on plant growth and nutrient content of soybean compared to TiO2; (2) that both Fe3O4 and TiO2 would alter communities of microbes that grow in close association with plants such as nitrogen-fixing bacteria as well as arbuscular mycorrhizal (AM) fungi; and (3) that the concentration and charge of the NP would affect plant uptake of NP in roots and translocation to above ground plant tissue such as leaves and stems
The as-synthesized Fe3O4 NPs were capped with oleic acid and were later functionalized with amine- or carboxylic acid-terminating ligands through a silane ligand-based exchange water phase transfer process
Summary
Metal oxide nanoparticles (NPs) are being increasingly used for commercial applications ranging from inclusion in self-cleaning coatings, topical sunscreens, and antimicrobial soaps [1,2,3,4,5]. Priester et al found that ZnO had relatively little effect on nitrogen-fixation in a soybean crop system, but CeO2 had significant negative effects on nitrogen fixation at medium and high concentrations [7] These studies suggest that toxic effects on soil microbes could be selective, and inhibition of certain microbial groups could alter soil microbial communities within the plant rhizosphere with negative consequences for plant nutrient uptake and soil fertility. We hypothesized that (1) treatment of soil with Fe3O4 would have fewer effects on plant growth and nutrient content of soybean compared to TiO2; (2) that both Fe3O4 and TiO2 would alter communities of microbes that grow in close association with plants (i.e., microbial symbionts) such as nitrogen-fixing bacteria (i.e., rhizobia) as well as AM fungi; and (3) that the concentration and charge of the NP would affect plant uptake of NP in roots and translocation to above ground plant tissue such as leaves and stems. The plant growth response was assessed by whole plant biomass and nutrient analysis, while root microbial community responses were determined using DNA-based methods or biomass measurements as needed
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