Nitrogen sources and CO concentration synergistically affect the growth and metabolism of tobacco plants.

The initial stimulation of photosynthesis under elevated CO concentrations (eCO) is often followed by a decline in photosynthesis, known as CO acclimation. Changes in N levels under eCO can have different effects in plants fertilized with nitrate (NO) or ammonium (NH) as the N source. NO assimilation consumes approximately 25% of the energy produced by an expanded leaf, whereas NH requires less energy to be incorporated into organic compounds.