Plant growth in elevated CO₂ alters mitochondrial number and chloroplast fine structure

With increasing interest in the effects of elevated atmospheric CO₂ on plant growth and the global carbon balance, there is a need for greater understanding of how plants respond to variations in atmospheric partial pressure of CO₂. Our research shows that elevated CO₂ produces significant fine structural changes in major cellular organelles that appear to be an important component of the metabolic responses of plants to this global change. Nine species (representing seven plant families) in several experimental facilities with different CO₂-dosing technologies were examined. Growth in elevated CO₂ increased numbers of mitochondria per unit cell area by 1.3-2.4 times the number in control plants grown in lower CO₂ and produced a statistically significant increase in the amount of chloroplast stroma (nonappressed) thylakoid membranes compared with those in lower CO₂ treatments. There was no observable change in size of the mitochondria. However, in contrast to the CO₂ effect on mitochondrial number, elevated CO₂ promoted a decrease in the rate of mass-based dark respiration. These changes may reflect a major shift in plant metabolism and energy balance that may help to explain enhanced plant productivity in response to elevated atmospheric CO₂ concentrations.