Foliar Applied ZnO Quantum Dots Boost Pumpkin (Cucurbita moschata Duch.) Growth and Positively Alter Endophytic and Rhizosphere Microbial Communities

Zinc oxide quantum dots can enhance pumpkingrowth by modulatingendophytic and rhizosphere microbial communities in nano-enabled agriculture. Systematic understanding of the impact of nanomaterials(NMs) onthe health and activity of plant-associated microorganisms is requiredfor sustainable development of efficient nano-enabled agrochemicals.Zinc (Zn) is an essential micronutrient for plant growth and development.It plays a vital role in various physiological processes, includingenzyme activation, protein synthesis, cell division, etc. The presentstudy investigated the effects of foliar exposure to different sizesof ZnO particles, including ZnO quantum dots (ZnO QDs, 4.06 nm), ZnOnanoparticles (ZnO NPs, 60.0 nm), bulk-scale ZnO particles (ZnO BPs,464.5 nm), and Zn ions at an equivalent Zn molar concentration (0.61mM) on the endophytic and rhizosphere microbial communities of pumpkinseedlings. ZnO QDs increased the total plant biomass by 24.6% as comparedto the control. ZnO QDs also increased the contents of total chlorophylland carotenoids, elevated micronutrient (Zn, Fe, and B) uptake, andtriggered the activities of antioxidant enzymes, such as peroxidase(POD), polyphenol oxidase (PPO), and catalase (CAT), as compared tocontrols. The composition and diversity of the endophytic and rhizospherebacterial or fungal communities were significantly altered as a functionof ZnO NM size, and a significant difference between the control andZnO treatments was also evident. Linear discriminant effect size analysis(LEfSe) shows that the putative beneficial host microbes Steroidobacter (relative abundance, RA: 1.05%) and Paenibacillus (RA: 0.59%) were enriched in pumpkin seedlings treated with ZnOQDs, which may lead to greater plant growth, nutrient acquisition,and stress resistance. Cooccurrence networks indicate that ZnO QDsincreased both node and link numbers of the bacterial networks by46.94 and 123.38% in the roots, which could further stabilize themicrobial community and confer resistance to environmental disturbance.Our overall findings demonstrate that ZnO QDs could enhance plantgrowth both directly by improving physiological performances and indirectlyby modulating beneficial endophytic and rhizosphere microorganisms.Thus, nano-enabled strategies can be a promising and sustainable approachto increase crop growth and resistance to stress.