Abstract: By using aeroponics culture system, this paper studied the effects of root zone hypoxia (10% and 5% O₂) stress on the root nitrogen metabolism of Cucumis melo during its fruit development period. During the 30 days experiment, the root NO₃^--N and NH₄⁺-N contents and nitrate reductase (NR) and glutamine synthetase (GS) activities of C. melo in treatments 10% and 5% O₂ decreased after an initial increase, as compared with the control (21% O₂). At the 20 days of hypoxia treatments, the abovementioned indicators were significantly higher than those of the control, while it they were adverse at the 30 days of hypoxia stress treatments. Moreover, the magnitude of the change was greater in treatment 5% O₂ than in treatment 10% O₂. The root glutamate dehydrogenase (GDH) activity at the 10 days of hypoxia stress treatments was significantly lower than that of the control, while the difference was not significant at the 20 days of hypoxia stress treatments. No significant difference was observed in the root glutamic acid oxaloacetate transaminase (GOT) activity among the hypoxia stress treatments at the 20 days, but the GOT activity was significantly lower than that of the control at the 30 days. The root glutamic acid-pyruvic acid transaminase (GPT) activity in treatment 5% O₂ at the 30 days and in 10% O₂ treatment at the 20 days was significantly lower than that of the control. During the 30 days experiment, the root soluble protein content and the total amino acid content and most amino acids in xylem sap decreased with the decrease of rhizosphere O₂ concentration. It was concluded that when the rhizosphere O₂ concentration during the fruit development period of muskmelon fall to 10%, the root nitrogen uptake and assimilation, amino acid synthesis, and nitrogen translocation of the muskmelon were inhibited.

Key words: natural Betula platyphylla forest, meteorological factor, individual tree diameter increment, regional effect.