Response of Xanthium strumarium leaf respiration in the light to elevated CO₂ concentration, nitrogen availability and temperature

• The leaf-level response of respiration in the light (R_L) is a vital component of a plant's energy and carbon balance. • Xanthium strumarium (common cocklebur) plants were grown in various combinations of CO₂, nitrogen and temperature, and R_L was measured using the Kok effect method. • R_L was significantly lower than respiration in the dark (R_D), with the lowest percentage inhibition in the elevated CO₂, high-N treatment. In general R_L increased in response to increased CO₂ concentration and N availability across all temperature treatments. However, there was a significant interactive effect of growth CO₂ concentration and measurement temperature on R_L which indicated that R_L responded more positively to temperature changes in elevated CO₂ conditions. Additionally, across all CO₂ and N treatments the percentage of respired C with respect to assimilated C increased as temperature increased. • Collectively, these results improve our understanding of the magnitude and sensitivity to foreseen environmental changes of mitochondrial respiration during light hours.