Investigation of the effects and mechanisms of manganese-based NMs on rice growth

Manganese-based (Mn-based) nanomaterials (NMs) have great potential as alternatives to conventional Mn fertilizers. Yet, its environmental risks and effects on plant growth are not completely well understood. This study investigated the physiological effects of manganese dioxide (MnO₂) and manganese tetroxide (Mn₃O₄) NMs on inter-root exposure (0-500 mg/L) of hydroponically grown rice. The results showed that on inter-root exposure, 50 mg/L Mn-based NMs promoted the uptake of mineral elements and enhanced the enzymatic activities of antioxidant systems (CAT and SOD) in rice, whereas 500 mg/L Mn₃O₄ NMs disrupted the mineral element homeostasis and led to phytotoxicity. The promotion effect of MnO₂ NMs was better, firstly because MnO₂ NMs treatment had lower Mn content in the plant than Mn₃O₄ NMs. In addition, MnO₂ NMs are more transported and absorbed in the plant in ionic form, while Mn₃O₄ NMs exist in granular form. MnO₂ NMs and Mn₃O₄ NMs both can be used as nano-fertilizers to improve the growth of rice by inter-root application, but the doses should be carefully selected.