Phytotoxicity of HNTs to rice (Oryza sativa L.): Effects on rice growth and development

The phytotoxicity of halloysite nanotubes (HNTs) to rice (Oryza sativa L.) was evaluated at several stages from germination, seedling growth to spike setting, and the seedling stage was selected to study the effect of HNTs on the growth of rice. Rice was cultured using different concentrations of HNTs dispersions and a blank control group was cultured with deionized water. It was found that HNTs did not affect the germination of rice seeds, and at the seedling stage, the low concentration of HNTs dispersion (0.1 mg mL^-1) promoted the growth of rice. This significantly increased the biomass and root system of rice seedlings and also promoted the development of stems and leaves of rice seedlings. However, high concentration of HNTs dispersion (100 mg mL^-1) had an inhibitory effect on rice growth, resulting in a significant decrease in rice biomass, causing oxidative damage (increase in H₂O₂ content and malondialdehyde content, and disruption of cell membrane permeability), and causing a decrease in chlorophyll content in rice. The rice seedlings treated with HNTs were transplanted into the soil, and it was found that all the rice could grow healthily. The growth trend was consistent with the seedling stage, and all groups of rice were able to produce spikes, which indicated that the effect of HNTs on rice was slight. In total, this work displayed the toxicity of HNTs to rice, which lays the foundation for the application of HNTs in agricultural field.