Pristine and Sulfidized Zinc Oxide Nanoparticles Promote the Release and Decomposition of Organic Carbon in the Legume Rhizosphere

Abstract

The effects and mechanisms of zinc oxide nanoparticles (ZnO NPs) and their aging products, sulfidized (s-) ZnO NPs, on the carbon cycling in the legume rhizosphere are still unclear. We observed that, after 30 days of cultivation, in the rhizosphere soil of Medicago truncatula, under ZnO NP and s-ZnO NP treatments, the dissolved organic carbon (DOC) concentrations were significantly increased by 1.8-to 2.4-fold compared to Zn 2+ treatments, although the soil organic matter (SOM) contents did not change significantly. Compared to Zn 2+ additions, the additions of NPs significantly induced the production of root metabolites such as carboxylic acids and amino acids and also stimulated the growth of microbes involved in the degradations of plant-derived and recalcitrant SOM, such as bacteria genera RB41 and Bryobacter, and fungi genus Conocybe. The bacterial co-occurrence networks indicated that microbes associated with SOM formation and decomposition were significantly increased under NP treatments. The adsorption of NPs by roots, the generation of root metabolites (e.g., carboxylic acid and amino acid), and enrichment of key taxa (e.g., RB41 and Gaiella) were the major mechanisms by which ZnO NPs and s-ZnO NPs drove DOC release and SOM decomposition in the rhizosphere. These results provide new perspectives on the effect of ZnO NPs on agroecosystem functions in soil−plant systems.

Driving Role of Zinc Oxide Nanoparticles with Different Sizes and Hydrophobicity in Metabolic Response and Eco-Corona Formation in Sprouts (Vigna radiata)

“…These behaviors can further trigger phytotoxicity and reactive oxidation species (ROS) bursts, while the antioxidant system acts as a pivotal defense mechanism to combat the stress response . Liu et al also emphasized that primitive and sulfided (aging-modified) ZnO NPs stimulated the emission of root metabolites in the legume Medicago truncatula and enriched plant-derived microbial taxa to modulate the carbon cycle . Given that these findings are related to plant physiology and lack discussion of the associated molecular mechanisms, an in-depth study of toxicity regulation by NP surface characteristics is necessary and urgent.…”

“…In natural ecosystems, plants continuously release complex root exudates, i.e., active metabolites containing organic acids, amino acids, proteins, sugars, and nucleic acids, during growth . The toxicological effects induced by different NPs can not only modify biological processes but also stimulate the release of root exudates, which inevitably interact with exposed NPs in the environment, possibly contributing to the generation of NP–corona complexes. Nevertheless, there is an enormous lack of research on the metabolism and corona evolution of root–nano systems under the modulation of NPs with different surface properties.…”