|Leakey, Andrew d b|
|Ainsworth, Elizabeth - Lisa|
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/7/2009
Publication Date: 3/3/2009
Citation: Leakey, Andrew D.B., Xu, Fangxiu., Gillespie, Kelly M., McGrath, Justin M., Ainsworth, Elizabeth A., Ort, Donald R. 2009. Genomic Basis for Stimulated Respiration by Plants Growing Under Elevated Carbon Dioxide. Proceedings of the National Academy of Sciences USA. 106:3597-3602. Interpretive Summary: Plants have a critical role in the exchange of carbon dioxide to the atmosphere through the processes of photosynthesis and respiration. It has been well documented that photosynthesis increases in C3 plants grown at elevated carbon dioxide concentrations; however, it is unknown how respiration is affected by elevated carbon dioxide concentrations. Soybean was grown at elevated carbon dioxide concentration under open air conditions for two consecutive growing seasons, and the molecular, biochemical and physiological adjustment of respiratory capacity was measured. Greater respiration rates in soybean were driven by increased expression of genes encoding many enzymes in the respiratory pathway. Greater rates of respiration were also supported by the additional carbohydrate available when plants were grown at elevated carbon dioxide concentrations. Current models of ecosystem responses to elevated carbon dioxide may not account for the significant increase in plant respiration. If all C3 plants respond to elevated carbon dioxide concentration with a similar increase in respiration, the modeled stimulation of net primary productivity would be reduced in magnitude by 7.4-11.1 petagrams of carbon per year, a flux similar to anthropogenically produced carbon dioxide.
Technical Abstract: The photosynthetic and respiratory exchanges of CO2 by plants with the atmposhere are both significantly larger than anthropogenic CO2 emissions, and these fluxes will change as growing conditions are altered by climate change. Understanding and modeling feedbacks in CO2 exchange is important to predicting future atmospheric [CO2] and climate change. While the stimulation of C3 photosynthesis in plants by growth at elevated [CO2] can be predicted with confidence, the nature of changes in respiration is less certain. This is in large part 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 CO2 enrichment experiment were investigated over two 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 are observed in the leaves of plants grown at elevated [CO2]. Greater respiratory quotient and leaf carbohydrate content at elevated [CO2] provide evidence that stimulated respiration was supported by the additional photoassimilate available from enhanced photosynthesis at elevated [CO2]. If elevated [CO2] at the middle to end of this century stimulated respiration in all terrestrial plants by 37%, it would offset the stimulation of photosynthesis and net primary productivity by approximately 7.4-11.1 PgCy*-1; a flux similar in size to current anthropogenically produced CO2.