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. RL was significantly lower than respiration in the dark (R,), 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 RL which indicated that RL 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.