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Root-derived CO(2) efflux via xylem stream rivals soil CO(2) efflux
Doug P Aubrey1, Robert O Teskey1
1Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green St, Athens, GA 30602-2152, USA.
The New Phytologist
|August 14, 2009
Summary
Forest tree roots transport significant carbon dioxide (CO2) internally through stems, challenging assumptions about belowground respiration. This internal CO2 flux suggests respiration rates may be much higher than previously estimated.
Area of Science:
- Forest ecology
- Plant physiology
- Biogeochemical cycles
Background:
- Belowground metabolism significantly impacts forest gross primary productivity.
- Current models may underestimate total respiration due to unaccounted internal CO2 fluxes.
Purpose of the Study:
- To investigate the internal transport of CO2 from tree roots to stems via the xylem.
- To quantify the magnitude of this internal CO2 flux in a forest ecosystem.
Main Methods:
- Utilized an experimental Populus deltoides plantation as a model system.
- Measured daily CO2 flux from root systems into the stem xylem.
- Compared internal CO2 transport with CO2 diffusion from the soil surface.
Main Results:
- CO2 transported upward from roots into stems via xylem (0.26 mol CO2 m(-2) d(-1)) was comparable to CO2 diffusing from the soil surface (0.27 mol CO2 m(-2) d(-1)).
- Estimated that twice the amount of CO2 from belowground respiration entered the xylem compared to diffusion into the soil.
- Indicated substantial carbohydrate consumption by belowground autotrophic respiration.
Conclusions:
- A significant portion of root-respired CO2 is transported internally via xylem, not solely diffusing into the soil.
- Challenges the existing paradigm of belowground CO2 release in forest ecosystems.
- Suggests a need to revise estimates of belowground respiration and its impact on carbon cycling.
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