Abstract: Broad-leaved Korean pine forest is the zonal vegetation in eastern mountains of northeast China, which accounting for a third of the China’s national forest. In order to understand the response of temperate dominant tree species Korean pine and main associated tree species Mongolian oak in broad-leaved Korean pine forest under future climate change conditions (air temperature rising, decrease in precipitation), a competition pot experiment of two-year old Korean pine seedlings and one-year old Mongolian oak seedlings under different soil water contents were conducted under completely random design in April 24, 2012. This experiment set up four experimental treatments, with eighteen seedling replicates for each treatment. Two levels of soil water content were respectively 75-85 percent of the soil water-holding capacity for the high level, and 50-60 percent of soil water-holding capacity for the low level. The competition treatments were six same seedlings in one pot for mono culture and three seedlings for each of the two species in one pot for mixed culture. We analyzed the photosynthetic and physiological parameters and changes in biomass allocation. The experimentation of a growing season showed that: (1)Soil water deficit treatment resulted in the decreases of the maximum net photosynthetic rate in both Korean pine and Mongolian oak seedlings, the reduction rate of Mongolian oak reached a significant level, while Korean pine did not. Drought caused the decline in water use efficiency in Mongolian oak, while it increased significantly in Korean pine. Soil water deficit also led to the decreases in lateral root biomass, stem biomass, leaf biomass and whole tree leaf area in Mongolian oak seedlings, but the increases in fine root biomass and root to shoot ratio of Korean pine seedlings. (2)Mixed culture treatment reduced the maximum net photosynthetic rate and water use efficiency of Mongolian oak seedlings, thereby reduced their stem and lateral root biomass. While for the Korean pine seedlings, mixed culture treatment also reduced their water use efficiency, but it increased the specific leaf area and whole tree leaf area of Korean pine seedlings and therefore had less impact on seedling growth. These results indicate that, Mongolian oak is more sensitive and rapid response to drought. Korean pine seedlings are more competitive than Mongolian oak seedlings in interspecific competition.

Key words: Quercus mongolica, Pinus koraiensis, interspecific competition, drought