Abstract: To investigate the effect of N deposition on soil respiration of temperate forests, a simulated atmospheric nitrogen (N) deposition experiment was conducted in three typical temperate forests in Dongling Mountain in Beijing. The three forests included oak forest (broadleaf forest), larch forest and pine forest (coniferous forest). In each forest, we set control and N addition treatments (10 g N·m^-2·a^-1, five times of current atmospheric N deposition) and four replicates (15 m × 15 m). N addition (NH₄NO₃) and soil respiration measurement were conducted in growing season. The results showed that N addition decreased the soil respiration rate of broadleaf forest but enhanced that in coniferous forest. Under the N enriched condition, the accumulation emission of soil respiration during the growing season decreased by 6.13 g C·m^-2 in oak forest while increased by 1.78 g C·m^-2 and 5.64 g C·m^-2 in larch and pine forests, respectively. However, the shortterm effect of N addition was not significant among three temperate forests. Moreover, soil respiration rate (P<0.001) and the accumulation emission of soil respiration (P<0.001) in growing season among different forests varied significantly in the order of oak forest > pine forest > larch forest. Soil temperature was the key factor regulating soil respiration in the control and N addition treatments, which resulted in an apparent seasonal variation of soil respiration. The twofactor model, involving soil temperature and moisture, well fitted the variation of soil respiration in response to the temperature and moisture in the three temperate forests, and explained the 47%-87% variation of soil respiration. Furthermore, N addition regulated to some extent the response of soil respiration to soil temperature and moisture, and soil respiration increased faster and was more sensitive under conditions of relatively higher temperature and lower moisture under N addition. These findings revealed the shortterm effects of N addition on soil respiration in different temperate forests in North China, however, its underlying mechanisms is still unclear.

Key words: positive feedback, intertidal wetland ecosystem, bimodality, biomass threshold, alternative stable state