Abstract: Increased nitrogen deposition and changed precipitation pattern are the two important factors of global change, while the in situ experiments studying how the two factors affect greenhouse gases CO₂ and CH₄ fluxes are still limited. Taking the temperate broadleaved Korean pine (Pinus koraiensis) forest in Changbai Mountains of Northeast China as the object, and by using static chambers, this paper studied the effects of nitrogen addition (50 kg N·hm^-2·a^-1) and changed precipitation regime (30% increase and decrease of precipitation) on the soil CO₂ and CH₄ fluxes. Nitrogen addition inhibited the soil CH₄ consumption, and even, converted the CH₄ consumption into CH₄ release. However, this inhibition effect only lasted for approximately 5 days. Nitrogen addition also affected the relationships between the CH₄ flux and environmental factors (soil temperature, pH, and clay content) to some extent. The changed precipitation regime had no significant effects on the CH₄ flux. Nitrogen addition decreased the CO₂ flux, with an average decrement of 27.4% after 4 years continuous nitrogen addition. It was predicted that the effects of longterm continuous nitrogen addition on the CO₂ flux would be increased with time, and reached the maximum after certain years of nitrogen addition. Oppositely, the effects of single time nitrogen addition would be decreased with time, and disappeared by the end of the 1month cycle. The inhibition effect of nitrogen addition on the CO₂ flux was negatively correlated with soil water filled pore space (WFPS) (P=0.022), and enhanced and extended at higher temperature. Nitrogen addition and precipitation change could possibly alter the temperature sensitivity of soil respiration. Our results indicated that the soil nitrogen in temperate forest in Changbai Mountains had not reached a threshold, and the future nitrogen deposition increase would inhibit the CO₂ release and CH₄ uptake. Overall, nitrogen addition would inhibit the soil carbon release.

Key words: chlorophyll fluorescence, antioxidase, osmotic adjustment., drought stress