Effects of varying nano-ZnO concentrations on the physiology, biochemistry, root exudate, and root microbial community of Agrostis stolonifera

Abstract

Nanomaterials find widespread applications, but their potential harm to the environment and ecology necessitates effective recycling methods. In this study, the effects of varying nano-ZnO concentrations (0–1000 mg kg⁻¹) on the Agrostis stolonifera's physiological and biochemical parameters, root exudation, and root-associated microbial communities were systematically examined. At concentrations below 500 mg kg⁻¹, nano-ZnO facilitated growth in root and leaf tissues. Conversely, higher concentrations led to a reduction in chlorophyll a, chlorophyll b, and carotenoid levels, potentially impairing photosynthetic efficiency. Concurrently, malondialdehyde levels in leaf tissues escalated with increasing nano-ZnO concentrations, while the activities of peroxidase, superoxide dismutase, and catalase initially increased before diminishing. SEM-Mapping and TEM analyses substantiated the transport of nano-ZnO within Agrostis stolonifera. At a concentration of 500 mg kg⁻¹ nano-ZnO, root and leaf tissues contained Zn at levels of 0.4 wt% and 3.0 wt%, respectively. Notably, increases in zinc accumulation within both root and leaf tissues correspond with escalating concentrations of nano-ZnO. High concentrations of nano-ZnO reduce the diversity of root exudates and modify the structural characteristics of the root microbial community. Conversely, a lower concentration of nano-ZnO (250 mg kg⁻¹) is associated with an increase in root species richness and diversity, as well as a heightened relative abundance of Gemmatimonas, Bradyrhizobium, Bryobacter, and Ammoniphilus. This study is the first report to provide critical insights into nano-ZnO behavior in Agrostis stolonifera and underscores the necessity for further investigations to elucidate root secretion mechanisms and microbial community dynamics.