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| Titel |
Transport of root-derived CO2 via the transpiration stream affects aboveground tree physiology |
| VerfasserIn |
J. Bloemen, M. A. McGuire, D. P. Aubrey, R. O. Teskey, K. Steppe |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062318
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| Zusammenfassung |
| Recent research on soil CO2 efflux has shown that belowground autotrophic respiration is
largely underestimated using classical net CO2 flux measurements. Aubrey & Teskey (2009)
found that in forest ecosystems a substantial portion of the CO2 released from root respiration
remained within the root system and was transported aboveground in the stem via
the transpiration stream. The magnitude of this upward movement of CO2 from
belowground tissues suggested important implications for how we measure above-
and belowground respiration. If a considerable fraction of root-respired CO2 is
transported aboveground, where it might be fixed in woody and leaf tissues, then
we 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 was transported upwards from the base of the tree
toward the top. During its ascent, the 13C label was removed from the 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 ±Â 0.10 % of the
label applied was lost to the atmosphere by stem and branch efflux higher in the trees.
Given that one-half of root-respired CO2 may follow this internal flux pathway
(Aubrey & Teskey, 2009), we calculated that up to 44% of the root-respired CO2 could
diffuse to the atmosphere once transported to the stem and branches. Thus, a large
portion of CO2 that diffuses 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 exchange approach to estimating above- and
belowground autotrophic respiration is inadequate. Accurate quantification of this
internal carbon flux is necessary to understand plant physiological mechanisms
and to explain variations in above-and belowground respiratory patterns, but these
results do not imply the necessity for a reevaluation of net CO2 flux at the ecosystem
level.
Reference:
Aubrey DP, Teskey RO (2009) Root-derived CO2 efflux via xylem stream rivals soil CO2
efflux. New Phytologist 184: 35-40. |
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