Cerium oxide nanomaterials improve cucumber flowering, fruit yield and quality: the rhizosphere effect

Abstract

Nanomaterials (NMs) have emerged as a promising tool in sustainable agriculture. This study investigates the ability of the rhizosphere effects of cerium oxide (CeO₂) NMs to enhance the growth and development of cucumber plants. Results demonstrated that 10 mg kg⁻¹ CeO₂ NMs optimally induced early flowering and improved the overall yield and quality of cucumber fruit. Interestingly, the introduction of 10 mg kg⁻¹ CeO₂ NMs into soil, in the absence of plants, largely altered the soil metabolites, elevating auxin (IAA), sugar molecules (e.g., mannose, trehalose and sucrose), indole, and amino acids (e.g., tryptophan, phenylalanine, and tyrosine) by 4.6–129.8%. These compounds could act as biostimulants to promote plant growth and development. Furthermore, the presence of plants enhanced the effects of CeO₂ NMs in promoting rhizosphere metabolites related to IAA synthesis pathways, and the rhizosphere microbiome (e.g., actinobacteria) was largely promoted, which was favorable for IAA transport and nutrient uptake in roots. The transport from rhizosphere and local synthesis of IAA in cucumber plant induced early flowering (5 days) with optimized carbohydrate allocation and promoted flower metabolism (amino acids, organic acids and flavonoids). The fruit yield was finally increased (by up to 28.5%), and the fruit quality was improved by increasing the content of vitamins (16.1%), sugars (54.6%), flavonoids (11.8–32.5%) and nutrient elements (27.6–93.1%). This study provides insights into the application of CeO₂ NMs and their rhizosphere regulation for sustainable agriculture.