ongoing climate changes can substantially impact soil nitrogen availability through its effects on other environmental conditions such as temperature, precipitation, and the frequency and intensity of extreme whether events, eventually altering the primary productivity of plants and ecosystems. effects of environmental changes on soil nitrogen cycling and availability vary with among season and ecosystem. nitrogen is a critical factor regulating the photosynthetic responses of plants to elevated [co2] as it is a main component in photosynthetic enzymes and apparatus. thus, changes in soil nitrogen availability will likely affect the ecophysiological responses to climate change, particularly elevated [co2] and the effects can change with species. a good understanding of how nitrogen supply affects the physiological and morphological responses of plants to elevated [co2] is critical for predicting plant performance under future climate conditions. this study examined the interactive effects of elevated [co2] and nitrogen (n) supply on the physiological and morphological responses in yellow birch (betula alleghaniensis britt.). seedlings were exposed to two levels of [co2] (ambient 400 µmol mol-1 versus elevated 1000 µmol mol-1 ), and five levels of n supply (25, 50, 100, 150, and 200 mg n l -1 ) for 4 months. seedling height, root collar diameter, specific leaf area, biomass, biomass allocation, and foliar gas exchange parameters were assessed. [...]