Abstract: A water culture experiment with controlled dissolved oxygen concentration was conducted to explore the effects of exogenous NO₃^- on the root function and enzyme activities related to nitrogen metabolism of cherry (Prunun cerasus × P. canescens) seedlings under hypoxia stress. Comparing with the control (7.5 mmol NO₃^-·L^-1), treatments 15  and 22.5 mmolNO₃^-·L^-1 made the materials for plant metabolism abundant, ensured the synthesis of enzyme proteins, increased root activity, maintained root respiration, improved the activities of enzymes related to nitrogen metabolism, such as nitrate reductase (NR), glutamine synthethase (GS), and glutamate dehydrogenase (NADH-GDH) in roots, and thereby, supplied enough energy for root respir
ation and NAD+ to glycolytic pathway, ensured electron transfer, and avoid ammonium toxicity under hypoxia stress. As a result, the injury of hypoxia stress to cherry plant was alleviated. Applying NO₃^-· at the concentration of 22.5 mmol·L^-1 was more advisable. However, NO₃^-· deficiency (0 mmol·L^-1) showed opposite results. The above results suggested that applying exogenousNO₃^-· to growth medium could regulate cherry root function and nitrogen metabolism, and antagonize the damage of hypoxia stress on cherry roots.

Key words: cherry, hypoxia stress, NO₃^- -N, root function, nitrogen metabolism, enzyme activity, city and town concentrated area, land use change, carbon emission, low-carbon regulation countermeasures.