Abstract:  Using leaf spraying method， water culture experiment was carried out for investigating the effects of different concentrations of fulvic acid （0.08%， 0.15% and 0.25%） on the growth and activities of nitrogen metabolism enzymes in pakchoi under NO-3 stress. The results showed that compared with the control， the growth was obviously restrained， photosynthetic pigment contents and activities of nitrogen metabolism enzymes were affected in pakchoi under NO-3 stress. Exogenous fulvic acid treatment could alleviate the damage on growth of pakchoi under NO-3 stress， the contents of photosynthetic pigment and the activities of nitrate reductase， glutamine synthetase， glutamate synthase and glutamate dehydrogenase were increased， contents of nitrate and ammonia were decreased. In conclusion， exogenous fulvic acid treatment could improve the growth and photosynthesis of pakchoi under NO-3 stress， promote plant nitrate uptake and utilization， and further alleviate the damage of pakchoi under NO-3 stress.

Key words: pakchoi, NO-3 stress, fulvic acid, nitrogen metabolism