Foliar Application of Zinc Oxide Nanoparticles Alleviates Phenanthrene and Cadmium-Induced Phytotoxicity in Lettuce: Regulation of Plant–Rhizosphere–Microbial Long Distance
Manman Cao, Wenxiao Lv, Fei Wang, Shuai Ma, Huanhuan Geng, Junhong Li, Ziqi Gao, Qing Xu, Guo Jing, Wenjun Leng, Ke Chen, Zhiqiang Tan, Peng Zhang, Ke Sun, Baoshan Xing
Abstract
Foliar application of beneficial nanoparticles exhibits potential in mitigating combined stresses from heavy metals and polycyclic aromatic hydrocarbons (PAHs) in crops, necessitating a comprehensive understanding of plant–rhizosphere–microbial processes to promote sustainable nanotechnology in agriculture. Herein, we investigated the mitigating mechanisms of foliar application of zinc oxide nanoparticles ( n ZnO) on lettuce growth under phenanthrene (Phe) and cadmium (Cd) costress. Compared to Phe + Cd treatment, low (L- n ZnO) and high (H- n ZnO) concentration of n ZnO increased fresh biomass (27.2% and 8.42%) and root length (20.4% and 39.6%) and decreased MDA (35.0% and 40.0%) and H 2 O 2 (29.0% and 15.6%) levels. L- n ZnO and H- n ZnO decreased Cd in roots (26.8% and 41.8%) and enhanced Zn in roots (19.9% and 107%), stems (221% and 2510%), and leaves (233% and 1500%), suggesting the long-distance migration of Zn from leaves to roots and subsequently regulating the metabolic pathways and microbial communities. Metabolomics revealed that n ZnO modulated leaf glycerophospholipid metabolism and amino acid pathways and promoted rhizosphere soil carbon and phosphorus metabolism. Additionally, n ZnO enriched the plant-growth-promoting, extreme, and stress-resistant bacteria in roots and leaves and heavy-metal-resistant and PAH-degrading bacteria in rhizosphere soil. These findings underscore the promising nanostrategy of n ZnO to benefit plant growth in soil cocontaminated with heavy metals and PAHs.