Genomic basis for stimulated respiration by plants growing under elevated carbon dioxide

Photosynthetic and respiratory exchanges of CO₂ by plants with the atmosphere are significantly larger than anthropogenic CO₂ emissions, and these fluxes will change as growing conditions are altered by climate change. Understanding feedbacks in CO₂ exchange is important to predicting future atmospheric [CO₂] and climate change. At the tissue and plant scale, respiration is a key determinant of growth and yield. Although the stimulation of C₃ photosynthesis by growth at elevated [CO₂] can be predicted with confidence, the nature of changes in respiration is less certain. This is largely because the mechanism of the respiratory response is insufficiently understood. Molecular, biochemical and physiological changes in the carbon metabolism of soybean in a free-air CO ₂ enrichment experiment were investigated over 2 growing seasons. Growth of soybean at elevated [CO₂] (550 μmol·mol ^-1) under field conditions stimulated the rate of nighttime respiration by 37%. Greater respiratory capacity was driven by greater abundance of transcripts encoding enzymes throughout the respiratory pathway, which would be needed for the greater number of mitochondria that have been observed in the leaves of plants grown at elevated [CO₂]. Greater respiratory quotient and leaf carbohydrate content at elevated [CO₂] indicate that stimulated respiration was supported by the additional carbohydrate available from enhanced photosynthesis at elevated [CO₂]. If this response is consistent across many species, the future stimulation of net primary productivity could be reduced significantly. Greater foliar respiration at elevated [CO₂] will reduce plant carbon balance, but could facilitate greater yields through enhanced photoassimilate export to sink tissues.