Abstract: The method of controlling dissolved oxygen concentration in nutrient solution was used. Effects of hypoxia on biomass of plant and root activity, respiratory rate, the activities of enzymes involved in nitrogen metabolism in the Malus hupehensis Rehd. seedling root system was studied. Results showed that the growth of seedling was inhibited and it was more serious as dissolved oxygen concentration of nutrient solution decreased under hypoxia; The respiratory rate of root system was more inhibited with decreasing dissolved oxygen concentration of nutrient solution first. But the inhibitory effect was decreased over the treatment time. The root activity was increased rapidly and then descended quickly; the activity of nitrate reductase (NR) and glutamine synthethase (GS) was improved under hypoxia. The activity of glutamate dehydrogenase (NADH-GDH) was inhibited first and then was promoted. The hypoxia was reduced probably by improving respiration consumption and changing the metabolic pathway.

Key words: Malus hupehensis Rehd., Hypoxia, Root activity, Enzymes, Nitrogen metabolism