The experiment studied how different nitrogen levels, CO2 concentrations, and temperatures affect the chlorophyll content in young Quercus mongolica seedlings. High nitrogen levels increased chlorophyll content, especially under elevated CO2 concentration. Elevated temperature increased chlorophyll a content but not chlorophyll b. Normal nitrogen levels showed no significant changes in chlorophyll content with CO2 or temperature. Without nitrogen, higher CO2 levels and temperature slightly increased chlorophyll a but not b. Elevated CO2 levels increased the need for nitrogen in the seedlings, while higher temperatures also increased nitrogen requirements to some extent.