Transport of root-respired CO₂ via the transpiration stream affects aboveground carbon assimilation and CO₂ efflux in trees

New Phytol. 2013 Jan;197(2):555-565. doi: 10.1111/j.1469-8137.2012.04366.x. Epub 2012 Oct 11.


Upward transport of CO₂ via the transpiration stream from belowground to aboveground tissues occurs in tree stems. Despite potentially important implications for our understanding of plant physiology, the fate of internally transported CO₂ derived from autotrophic respiratory processes remains unclear. We infused a ¹³CO₂-labeled aqueous solution into the base of 7-yr-old field-grown eastern cottonwood (Populus deltoides) trees to investigate the effect of xylem-transported CO₂ derived from the root system on aboveground carbon assimilation and CO₂ efflux. The ¹³C label was transported internally and detected throughout the tree. Up to 17% of the infused label was assimilated, while the remainder diffused to the atmosphere via stem and branch efflux. The largest amount of assimilated ¹³C was found in branch woody tissues, while only a small quantity was assimilated in the foliage. Petioles were more highly enriched in ¹³C than other leaf tissues. Our results confirm a recycling pathway for respired CO₂ and indicate that internal transport of CO₂ from the root system may confound the interpretation of efflux-based estimates of woody tissue respiration and patterns of carbohydrate allocation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Air
  • Biological Transport
  • Biomass
  • Carbon / metabolism*
  • Carbon Dioxide / metabolism*
  • Carbon Isotopes
  • Cell Respiration
  • Isotope Labeling
  • Plant Leaves / metabolism
  • Plant Roots / cytology
  • Plant Roots / metabolism*
  • Plant Stems / metabolism
  • Plant Transpiration / physiology*
  • Trees / anatomy & histology
  • Trees / metabolism*


  • Carbon Isotopes
  • Carbon Dioxide
  • Carbon