MOLECULAR MECHANISMS AND MULTI-OMICS INSIGHTS INTO OXYGEN NANOBUBBLE-ENRICHED DEFICIT FERTIGATION FOR ENHANCING RESOURCE-USE EFFICIENCY AND FRUIT QUALITY IN GREENHOUSE CUCUMBER

Abstract

Oxygen nanobubble-enriched fertigation is a newly developed strategy for improving available oxygen in the rhizosphere and crop performance under limited irrigation; however, its physiological and molecular effects in greenhouse cucumber remain unclear. This study tested the effect of oxygen nanobubble-enriched deficit fertigation on growth, yield, resource-use efficiency, fruit quality, oxidative stress regulation, and multi-omics responses of cucumber (Cucumis sativus L.) under greenhouse conditions. A total of five fertigation treatments were compared: full irrigation with conventional fertigation (control); 75% deficit irrigation with conventional fertigation; full irrigation with oxygen nanobubble fertigation; 75% deficit irrigation with oxygen nanobubble fertigation; and 60% deficit irrigation with oxygen nanobubble fertigation. Oxygen nanobubble enrichment significantly raised the root-zone dissolved oxygen and alleviated the negative impacts of deficit irrigation on photosynthesis, root growth, and yield. Among treatments, 75% deficit irrigation combined with oxygen nanobubble fertigation was the most promising, as it retained yields near full-irrigation levels while enhancing water productivity, nitrogen-use efficiency, marketable yield, fruit firmness, soluble solids, vitamin C, phenolics, and antioxidant activity. Additionally, this treatment lowered nitrate accumulation in fruit, hydrogen peroxide, malondialdehyde, and electrolyte leakage, and increased antioxidant enzyme activities. The gene expression analysis indicated that genes related to aquaporins, nutrient transporters, antioxidants, oxygen-responsive factors, and stress-regulatory factors were upregulated. Additional metabolomic and rhizosphere analyses revealed improved carbon metabolism, Osmo protective adjustments, accumulation of antioxidant metabolites, and increased abundance of beneficial microbes. Overall, oxygen nanobubble-enriched fertigation at 75% irrigation optimizes cucumber yield, fruit quality and resource-use efficiency through coordinated physiological, biochemical, molecular, metabolic, and rhizosphere regulation.