Abstract: By using aeroponics culture system, this paper studied the impacts of root-zone hypoxia（10% O₂ and 5% O₂）stress on the plant growth, root respiratory metabolism, and antioxidative enzyme activities of muskmelon at its fruit development stage. Root-zone hypoxia stress inhibited the plant growth of muskmelon, resulting in the decrease of plant height, root length, and fresh and dry biomass. Comparing with the control (21% O₂), hypoxia stress reduced the root respiration rate and malate dehydrogenase (MDH) activity significantly, and the impact of 5% O₂ stress was more serious than that of 10% O₂ stress. Under hypoxic conditions, the lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and the malondialdehyde (MDA) content were significantly higher than the control. The increment of antioxidative enzyme activities under 10% O₂ stress was significantly higher than that under 5% O₂ stress, while the MDA content was higher under 5% O₂ stress than under 10% O₂ stress, suggesting that when the rootzone oxygen concentration was below 10%, the aerobic respiration of muskmelon at its fruit development stage was obviously inhibited while the anaerobic respiration was accelerated, and the root antioxidative enzymes induced defense reaction. With the increasing duration of hypoxic stress, the lipid peroxidation would be aggravated, resulting in the damages on muskmelon roots, inhibition of plant growth, and decrease of fruit yield and quality.

Key words: root-zone hypoxia stress, muskmelon, respiratory metabolism, antioxidative enzyme activity, near infrared spectroscopy, soluble sugar to nitrogen ratio, partial least squares, back-propagation neural network, wavelet neural network.