[Effects of nitrogen deposition on leaf physiological and ecological characteristics of Lindera aggregata seedlings]

From June 2010 to July 2011, a pot experiment was conducted to explore the effects of nitrogen deposition on the leaf physiological and ecological characteristics of Lindera aggregate seedlings. Three levels of NH4NO3, i. e., low-N (2 g x m(-2) x a(-1)), medium-N (8 g x m(-2) x a(-1)), and high-N (32 g x m(-2) x a(-1)) , were added to simulate nitrogen deposition, and the seedling leaf photosynthesis, relative chlorophyll content, chlorophyll fluorescence parameters, membrane lipid peroxidation, and antioxidant enzyme activities were determined. After one-year treatment, the daily mean values of the net photosynthetic rate (P)n)) and the maximum net photosynthetic rate (P(n max)) at low, medium and high levels of NH4 NO3 addition were 47.0%, 117.8% and 41.2%, and 82.6%, 191.3% and 152.2% higher than those of the control (no NH4 NO3 addition), respectively, with the highest values at medium level of NH4NO3 addition. The intercellular CO2 concentration, daily mean stomatal conductance, light saturation point, and apparent quantum yield in the three treatments of NH4NO3 addition were all higher than those of the control, and the dark respiration rate was the highest in treatment high-N. The relative chlorophyll content was the highest in treatment medium-N, followed by in treatment high-N, and had no significant difference between treatment low-N and the control. The chlorophyll fluorescence parameters varied with the levels of NH4NO3 addition. The PS II primary chemical efficiency (F(v)/F(m)) and PS II potential activity (F(v)/F(o)) were the lowest in treatment high-N, the superoxide dismutase activity was higher in nitrogen addition treatments than in the control, and the peroxidase activity, malonydialdehyde content, and membrane permeability were the highest in treatment high-N. All the results suggested that nitrogen deposition enhanced the photosynthetic ability of L. aggregata seedlings, with the most obvious effects in treatment medium-N, and altered the other physiological traits of the seedlings to different degrees.