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 (MnO) and manganese tetroxide (MnO) 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 MnO NMs disrupted the mineral element homeostasis and led to phytotoxicity. The promotion effect of MnO NMs was better, firstly because MnO NMs treatment had lower Mn content in the plant than MnO NMs. In addition, MnO NMs are more transported and absorbed in the plant in ionic form, while MnO NMs exist in granular form. MnO NMs and MnO 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.