Effects of Basal Fertilization Supplemented with Graphene and/or Microbial Inoculants on Growth and Fruit Quality of Winter Jujube Based on Metabolomics Analysis

Winter jujube is highly favored by consumers, and improving both the fruit quality and yield during cultivation is a key issue in horticultural research. Fertilization is a critical measure regulating growth. This study aimed to evaluate the effects of basal fertilizer combined with two novel synergistic additives—graphene and microbial inoculants—on the growth, fruit quality, and metabolic profiles of winter jujube, providing new fertilization strategies. The selected doses of graphene (0.38 g/plant) and microbial inoculant (0.26 g/plant) were based on the previous literature to balance efficacy, cost, and environmental safety. The graphene used was functionalized graphene oxide provided by Shanxi Datong University, chosen for its enhanced dispersibility and plant compatibility. Although this study focused on physiological and metabolic responses, the economic feasibility and potential environmental implications of these additives are discussed in the context of sustainable jujube production. Six-year-old winter jujube trees were treated with four fertilization regimes: basal fertilizer + graphene (T1), basal fertilizer + microbial fertilizer (T2), basal fertilizer + graphene + microbial fertilizer (T3), and basal fertilizer only (CK). Growth indices, mineral element contents in different organs, and fruit quality traits were measured. Widely targeted metabolomics was used to analyze metabolic variations among treatments. Compared with CK, all three synergistic fertilizer treatments tended to promote growth, increasing leaf area, chlorophyll content, and jujube bearing shoot length; contributed to the accumulation of P, K, Ca, Mg, and other minerals in various organs; and helped improve fruit quality by increasing the total sugars and flavonoids. T1 and T3 exhibited relatively better overall performance. Metabolomic analysis revealed significant differences in the metabolite profiles of winter jujube fruits across different treatments. Phenolic acids and flavonoids were closely associated with the improvement in fruit quality; further screening identified seven differential metabolites, predominantly belonging to phenolic acids. Basal fertilizer combined with graphene alone or with microbial inoculants may effectively promote growth and improve fruit quality by optimizing mineral uptake and regulating metabolic processes. These findings provide potential theoretical and practical support for high-quality, high-yield fertilization strategies for winter jujube.