In addition to dispersing into the soil and, ultimately, out into the atmosphere, carbon dioxide produced by tree roots can travel up the stem. The presence of this newfound pathway suggests that scientists have underestimated the amount of energy consumed by underground forest metabolism.
Doug Aubrey and Robert Teskey from the University of Georgia in Athens measured CO2 levels in the soil as well as in sap and water taken up by four eastern cottonwoods (Populus deltoides) at an experimental plantation in South Carolina. They estimated that twice as much CO2 entered the stem's xylem as diffused into the soil, providing evidence that below-ground respiration might exceed that by leaves and woody tissue.
Although preliminary, the study suggests that scientists need to reconsider the way they calculate forest carbon budgets.
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Phytology: Tree carbon recalibrated?. Nature 460, 554 (2009). https://doi.org/10.1038/460554b
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DOI: https://doi.org/10.1038/460554b
