<p>Rhizosphere CO₂ concentration is affected by multiple factors in agricultural production. When it exceeds a defined threshold, the growth of oriental melon seedlings will be suppressed, giving rise to metabolic dysfunctions that undermine the yield and quality of oriental melons. Hence, it is indispensable to identify efficacious mitigation approaches to cultivating high-quality oriental melons in controlled settings. Recent investigations have manifested that exogenous γ-aminobutyric acid (GABA) plays a crucial role in mediating responses to abiotic stress; however, the mechanisms which through GABA regulates nitrogen metabolism remain elusive under elevated rhizosphere CO₂ concentration. This study adopted an automatic rhizosphere CO₂ treatment system, with normal atmospheric CO₂ concentration of 0.037% as the control, rhizosphere CO₂ concentration of 1% as the stress treatment (T), and exogenous spraying of 50&#xa0;mmol/L GABA as the mitigation treatment (TG) under CO₂ stress conditions. The results showed that the elevated rhizosphere CO₂ concentration significantly inhibited the nitrogen metabolism of oriental melon seedlings. The ¹⁵N tracer technology verified that foliar spray of 50&#xa0;mmol/L GABA greatly improved the nitrogen uptake and distribution capacity of oriental melon seedlings under the condition of elevated rhizosphere CO₂ concentration. In addition, 50&#xa0;mmol/L exogenous GABA significantly increased the nitrogen assimilation utilization and nitrogen metabolism-related enzyme activities of oriental melon seedlings under elevated rhizosphere CO₂ concentration, and significantly up-regulated the expression levels of key enzyme genes and nitrogen transporter genes of nitrogen metabolism. In conclusion, when oriental melon seedlings were subjected to high CO₂ stress in rhizosphere, the nitrogen metabolism inhibited by elevated rhizosphere CO₂ concentration could be alleviated by exogenous application of 50&#xa0;mmol/L GABA.</p>