Abstract: [Objective]In this study, we investigated the effects of nitrogen (N) deposition and drought stress on the growth of Phyllostachys edulis seedlings, and explored physiological response mechanism of the seedlings to drought stress under different N deposition levels, which would be expected to provide a theoretical basis and technical support for the management and cultivation of P. edulis under the background of atmospheric N deposition.[Method]Two water conditions (normal water supply W, drought stress D) and four nitrogen deposition levels (nitrogen-free CK, low-nitrogen LN, Medium-nitrogen MN and high-nitrogen HN) were set up in a two-factors completely randomized experimental design. The variations of total biomass, leaf electrolyte leakage rate, malondialdehyde content, osmotic regulation substance content, and protective enzyme activity of seedlings of P. edulis under different treatments were analyzed.[Result]Drought stress resulted in significant increases of relative conductivity (by 16.8%) and malondialdehyde (by 35.1%) content in leaves compared with normal water condition, and hence restrained seedling growth, especially seedling mass. However, at the same time the proline content and protective enzyme activities were significantly increased, which to a certain extent mitigated the damage of drought stress to seedling growth. The effects of different N deposition levels on above parameters varied with water conditions. Under normal water condition, seedling mass increased with N deposition levels, while the proline content, electrolyte leakage rate and malondialdehyde content decreased firstly and then increased. And the tendency became more obvious with the extension of experimental time. Nitrogen deposition significantly increased superoxide dismutase (SOD) and peroxidase (POD) activity, but had no effect on catalase (CAT) activity. Under drought stress, seedlings mass also increased with N deposition levels, but tended to decrease when the N deposition level was higher than 60 Kg ha^-1a^-1,The effects of N deposition on proline content, the electrolyte leakage rate and malondialdehyde content in leaves were similar to those under normal water condition, whereas the three protective enzymes activities increased firstly and then decreased with N deposition levels, resulting in the enzyme activities in seedlings under the D-HN treatments the lowest.[Conclusion]Drought stress inhibited the growth of P. edulis seedlings. The N deposition levels of 30 kg·hm^-2a^-1 and/or 60 kg·hm^-2a^-1 increased the activities of protective enzymes, decreased the degree of membrane lipid peroxidation, alleviated the inhibition of drought stress on the growth of P. edulis seedlings, and thus, improved the drought resistance of P. edulis. However, a high rate of N deposition (i.e. 90 kg·hm^-2a^-1) was not able to alleviate the degree of membrane lipid peroxidation, and even further aggravated the damage of drought stress.

Key words: Phyllostachys edulis, drought stress, nitrogen deposition, lipid peroxidation, protective enzyme activity