Mechanism of cerium oxide nanomaterials promoting wheat germination in different soils: the role of recruited microorganisms

Abstract

Seed germination is a critical and environmentally sensitive stage. Cerium oxide nanomaterials (CeO₂ NMs) have been proven to enhance crop productivity. However, it remains unclear how soil microbes mediate the effects of CeO₂ NMs on germination in different soils. In this study, four soils applied with different concentrations of CeO₂ NMs were studied. Ten mg L⁻¹ CeO₂ NMs significantly promoted wheat growth in yellow-brown soil, red soil, and fluvo-aquic soil (sandy soil), while 50 mg L⁻¹ was optimal for fluvo-aquic soil (garden soil), indicating the promotion effect relates to both NM concentration and soil type. The germination index, root length, and chlorophyll content were highest in sandy soil. Partial least squares path modeling (PLS-PM) analysis showed that soil physicochemical properties shaped bacterial communities, which in turn impact wheat seed germination and growth. CeO₂ NMs upregulated the abundances of beneficial bacteria (Pseudomonas, Massilia, Ramlibacter, Bacillus, and Enterobacter) by 28.5–576.6% (without seeds) and 22.1–132.7% (with seeds), creating favorable soil conditions for germination. The beneficial bacteria were recruited by increasing soil organic acids, fatty acids, amino acids, and nucleotides by 2.12–4.09-fold. CeO₂ NMs also entered seeds; NMs increased α-amylase activity (28.4–69.6%) and soluble sugar content (20.7–33.8%) to supply germination energy. The phytohormone levels were also altered, with increasing gibberellin (6.6–13.4%) and auxin (16.8–34.3%) and decreasing abscisic acid (10.7–18.9%) while enhancing the tricarboxylic acid (TCA) cycle and glycolysis. Wheat grows optimally in sandy soil due to its rich nutrients, with CeO₂ NMs upregulating more soil metabolites that recruit Bacillus and Massilia. This microbial mediation also achieves the highest levels of seed gibberellin (GA) and α-amylase activity, collectively promoting growth. This study offers insights into the microbial-mediated promotion of wheat seed germination for sustainable agricultural practices and also provides a basis for assessing the potential environmental impacts of CeO₂ NMs in agricultural ecosystems.