This study performed physiological, transcriptome, and metabolite analyses of peach fruit under different nitrogen (N) conditions at different growth stages. Nitrogen management directly affected the yield, fruit quality, and metabolites of peach in different growth stages. Different fertilizing time influenced yield and leaf N concentration. RNA-Seq was used to analyze the influence of N levels at the fruit pit hardening (PH) and fruit expansion (FE) stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed differentially expressed genes (DEGs) related to carbon and nitrogen metabolite processes. Metabolome analysis shows that applying different nitrogen fertilizers at different growth stages of peach mainly affected metabolites related to carbon and amino acids. This research provides insight into the metabolic processes underlying different N responses during different growth stages and provides a foundation to improve the efficiency of N use in peach.

Pre-harvest nitrogen (N) application has been proven effective for improving fruit yield and quality. However, a full understanding of how differences in N availability/plant N status influence the transcriptome and metabolism underlying yield formation and quality remains elusive. Here, a combined analysis of the morpho-physiological qualities, transcriptome, and metabolite of peach plants was performed under different nitrogen levels at fruit pit hardening (PH) and fruit expansion (FE). Nitrogen fertilizer directly affected the yield, fruit quality, and metabolites of peach at different growth stages. RNA-Seq was used to analyze the influence of N levels at PH and FE in peach. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the differentially expressed genes (DEGs) focused on flavonoid biosynthesis and secondary metabolite biosynthetic processes. The differential metabolites among the different treatments were mainly involved in flavonoid metabolism. Transcriptome analysis showed that applying different nitrogen fertilizers at different growth stages of peach mainly affected the synthesis of flavonoids in fruit. Overall, these results suggest that the impacts of pre-harvest N application on fruit yield and quality differ between developmental stages. This research provides a full understanding of the metabolic processes underlying fruit growth and development in peach, providing a theoretical basis for the improvement of nitrogen use efficiency in peach trees.