Collaborative Research: Controls on the Isotopic Composition of Fixed CO2 and Ecosystem-Respired CO2 in Southeastern Pine Forests

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Ever since scientists linked human production of carbon dioxide with global warming, they have sought to quantify how much impact humans have had on climate. Half the CO2 produced by humans-mainly from the burning of fossil fuels-remains in the atmosphere. The other "missing half" is either adsorbed by the oceans or taken up by terrestrial plants during photosynthesis. Knowing how much goes where is a crucial link in understanding how human activity affects global climate and the global carbon cycle. A useful marker to trace the destination of CO2 is the ratio of 13C to 12C in CO2 in the air. Land plants preferentially take up 12C, enriching the air in 13C. The oceans don't discriminate when they take up CO2. So by measuring the ratio of 13C to 12C, scientists can tell whether the CO2 is going into land plants or into the ocean. But there is variation in how much 13C to 12C land plants take up, so the models that predict where human-produced CO2 winds up can have significant error. To limit the error, and develop better estimates of the fate of CO2, a new study will be conducted to examine southern pine forests, one of the largest carbon sinks in North America. The study will look at how climate variability affects the 13C/12C ratio of the CO2 that plants absorb and release during their respiration. The result may yield a significant recalculation of how important land plants are as a "sink" for human-produced CO2.The study will look at carbon isotope composition in leaf waxes and respired CO2. This will be used to improve estimates of the distribution and magnitude of the terrestrial carbon sink, a step in further understanding the importance of land plants as absorbers of CO2 produced by humans.