Metabolomics Analysis Reveals the Mechanism of Hydrogen Cyanamide in Promoting Flower Bud Break in Blueberry

Bud dormancy of deciduous fruit trees is a complex process that allows trees to survive long periods in adverse conditions during winter. Dormancy is a major obstacle for both fruit production in mild winter areas and off-season culture of fruit trees in protection facilities. It is very economically advantageous to be able to control the time point of bud break and consequently harvest in crops with high returns and short harvest seasons like blueberry (Vaccinium spp.). Hydrogen cyanamide (H2CN2 (HC)) treatment is an effective method to promote dormancy release and synchronize bud break in perennial deciduous fruit trees, including blueberry. However, there are few systematic studies of the metabolic changes that occur during HC-induced bud breaking. In this study, the metabolome of blueberry buds under forced conditions following HC and water treatment (control) was analyzed using gas chromatography paired with time-of-flight mass spectrometry (GC–TOFMS) technology. A total of 252 metabolites were identified and 16 differential metabolites (VIP > 1, p < 0.05) were detected. The levels of several soluble sugars (fructose, glucose, maltose), organic acids (citric acid, alpha-ketoglutaric, succinic acid), and amino acids (aspartic acid, glutamic acid, phenylalanine) were upregulated, while tyrosine, tryptophan, and asparagine were significantly downregulated in HC-treated buds when compared with control buds. The synthesis and accumulation of phenylpropanoids (salicin, 4-vinylphenol, neohesperidin) were also promoted by HC. These results suggest that alteration of carbohydrate and amino acid metabolism, tricarboxylic acid (TCA) cycle increase, and phenylpropanoid accumulation were crucial in HC-promoted bud breaking in blueberry. This research extends our understanding of the mechanisms involved in dormancy release induced by HC and provides a theoretical basis for applying HC to accelerate bud break.