It was found that the CO2 elevation stimulated photosynthesis to a much larger extent in both species when they grew together as compared to growing separately. There was a significant Temperature x Nutrient x Species effect on photosynthetic rate in the mixture experiment. White spruce responded positively to warmer soil temperature and higher nutrient supply by increasing photosynthetic rate while the photosynthesis of black spruce did not show a significant response. In the mono experiment, the 4 factors had significant interactive effect on nitrogen use efficiency (NUE). Overall, elevated [CO2] enhanced NUE in black spruce irrespective of the temperature-nutrient treatment while it increased NUE in white spruce only in the high nutrient treatment. In the mixture experiment, there were significant CO2 x Nutrient and CO2 x Species effects. CO2 elevation increased NUE in seedling grown in the low nutrient treatment. CO2 elevation enhanced NUE more in black spruce than in white spruce. The species responded differently to nutrient supply, with black spruce being more efficient in utilising nutrients. Growth in mixture increased CO2 elevation enhancement on photosynthetic rate indicating more efficient resource utilisation.