Aubrey, Doug P

Bloemen, Jasper

McGuire, Mary Anne

Steppe, Kathy

Teskey, Robert O

English

Ghent University Academic Bibliography

Geophysical Research AbstractsVol. 14, EGU2012-4391-2, 2012EGU General Assembly 2012© Author(s) 2012Transport of root-derived CO2 via the transpiration stream affectsaboveground tree physiologyJ. Bloemen (1), M.A. McGuire (2), D.P. Aubrey (2), R.O. Teskey (2), and K. Steppe (1)(1) Laboratory of Plant Ecology, Ghent University, Coupure links 653, 9000 Gent, Belgium (jasper.bloemen@ugent.be), (2)Warnell school of Forestry and Natural Resources, University of Georgia,180 East Green St, Athens, GA, 30602-2152, USARecent research on soil CO2 efflux has shown that belowground autotrophic respiration is largely underestimatedusing classical net CO2 flux measurements. Aubrey & Teskey (2009) found that in forest ecosystems a substantialportion of the CO2 released from root respiration remained within the root system and was transported abovegroundin the stem via the transpiration stream. The magnitude of this upward movement of CO2 from belowground tis-sues suggested important implications for how we measure above- and belowground respiration. If a considerablefraction of root-respired CO2 is transported aboveground, where it might be fixed in woody and leaf tissues, thenwe are routinely underestimating the amount of C needed to sustain belowground tissues.In this study, we infused 13C labeled water into the base of field-grown poplar trees as a surrogate for root-respired CO2 to investigate the possible role of root-derived CO2 as substrate for carbon fixation. The label wastransported upwards from the base of the tree toward the top. During its ascent, the 13C label was removed fromthe transpiration stream and fixed by chlorophyll-containing woody (young bark and xylem) and leaf (petiole)tissues. Moreover, based on 13C analysis of gas samples, we observed that up to 88 ± 0.10 % of the label appliedwas lost to the atmosphere by stem and branch efflux higher in the trees. Given that one-half of root-respired CO2may follow this internal flux pathway (Aubrey & Teskey, 2009), we calculated that up to 44% of the root-respiredCO2 could diffuse to the atmosphere once transported to the stem and branches. Thus, a large portion of CO2 thatdiffuses out of aboveground tissues may actually result from root respiration.Our results show that CO2 originating belowground can be transported internally to aboveground parts of trees,where it will have an important impact on tree physiology. Internal transport of CO2 indicates that the gas exchangeapproach to estimating above- and belowground autotrophic respiration is inadequate. Accurate quantification ofthis internal carbon flux is necessary to understand plant physiological mechanisms and to explain variations inabove-and belowground respiratory patterns, but these results do not imply the necessity for a reevaluation of netCO2 flux at the ecosystem level.Reference:Aubrey DP, Teskey RO (2009) Root-derived CO2 efflux via xylem stream rivals soil CO2 efflux. New Phytologist184: 35-40.

Transport of root-derived CO2 via the transpiration stream affects aboveground tree physiology

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Transport of root-derived CO2 via the transpiration stream affects aboveground tree physiology

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