Nitrogen (N) is an essential element for plant growth and development. In this study, physiological, transcriptome and metabolite analyses of apple leaves and roots were compared under different N conditions. The results indicated that different N stresses influenced plant growth, the content of soil plant analytical development (SPAD) value and photosynthesis in apple seedlings. The content of hydrogen peroxide (H₂O₂), and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamine antinotransferase (GOGAT) were also affected by different N stresses. RNA-Seq was used to analysis the influence of different N tolerances in apple seedlings. Gene Ontology (GO) analysis of differentially expressed genes (DEGs) indicated that apple trees might affect the responses to photosynthesis, organic hydroxy compound biosynthetic process, and secondary metabolite biosynthetic process under N stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs focused on photosynthesis and secondary metabolite biosynthetic process. There were 527 differential metabolites in LNL/CKL, 157 in HNL/CKL, 477 in LNR/CKR, and 232 in HNR/CKR. The metabolome analysis indicated that total of 1004 and 389 significant differential metabolites were identified under low N and high N conditions in apple. Apple seedlings regulate the carbon metabolism, nitrogen metabolism and flavonoid pathway to adapt the different nitrogen environments. This research provide understanding for the metabolic processes underlying different N responses and provide a foundation for improving the efficiency of N use in apple trees.

氮（N）是植物生长发育的必需元素。本研究比较了不同施氮条件下苹果叶和根的生理、转录组和代谢物分析。结果表明，不同的氮胁迫影响了苹果幼苗的植物生长、土壤植物分析发育（SPAD）值和光合作用的含量。过氧化氢含量（H ₂ O ₂)，超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、硝酸还原酶(NR)、亚硝酸还原酶(NiR)、谷氨酰胺合成酶(GS)和谷氨酰胺抗转移酶(GOGAT)的活性也受到不同程度的影响。 N 强调。RNA-Seq用于分析不同N耐受性对苹果幼苗的影响。差异表达基因（DEGs）的基因本体（GO）分析表明，苹果树可能会影响氮胁迫下对光合作用、有机羟基化合物生物合成过程和次生代谢物生物合成过程的响应。京都基因和基因组百科全书 (KEGG) 通路分析表明，DEG 专注于光合作用和次级代谢物的生物合成过程。LNL/CKL 中有 527 种差异代谢物，HNL/CKL 中有 157 种，LNR/CKR 中有 477 种，HNR/CKR 中有 232 种。代谢组学分析表明，在低氮和高氮条件下，苹果共鉴定出 1004 和 389 种显着差异代谢物。苹果幼苗通过调节碳代谢、氮代谢和黄酮途径来适应不同的氮环境。该研究为理解不同氮响应背后的代谢过程提供了理解，并为提高苹果树中氮的利用效率提供了基础。