Effects of nZnS vs. nZnO and ZnCl2 on mungbean [Vigna radiata (L.) R. Wilczek] plant and Bradyrhizobium symbiosis: A life cycle study

Abstract

Scarce of knowledge of using Zinc (Zn) nanoparticles (NPs) to augment plant growth, Zn availability to plants and its potential toxicity warrants more NPs–plant life cycle studies. The main objectives of this study were to compare nano zinc sulphide (nZnS) with nano zinc oxide (nZnO) and ionic Zn i.e., ZnCl₂, as a source of Zn, as well as to establish physiological impact of NPs on growth, yield and symbiosis of mungbean [Vigna radiata (L.) R. Wilczek] plants at different concentrations (0, 0.01, 0.1, 1 and 10 mg kg⁻¹ of soil). In this study, mungbean plants were grown for 60 days (life cycle study) in natural soil infested with Bradyrhizobium. Effects of Zn compounds (nZnS, nZnO and ZnCl₂) on plant height, dry biomass, number of nodules per plant, yield and fruit agronomical parameters along with micronutrient assessment were determined. Impact of Zn compounds on Bradyrhizobium–mungbean symbiosis was also unravelled. Results showed that both the NPs, (nZnS and nZnO) were more effective than ZnCl₂ in promoting growth and yield up to a critical concentration and above which phytotoxic effects were observed. Both the NPs were more effective than ZnCl₂ at increasing fruit Zn content also. Whereas, nZnS treatment was found to be better than nZnO in improving overall plant growth. Bradyrhizobium–mungbean symbiosis was not affected at lower NPs concentrations, while higher concentration revealed toxicity by damaging bacterial morphology and nodule formation. There was no nano specific toxicity found while, ZnCl₂ showed relatively more toxicity than both the NPs. The present investigation demonstrated the concept of nano-micronutrient as well as NPs phytotoxicity by understanding NPs–plant interactions in the soil environment.