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| Titel |
The importance of internal CO2 gradients in tree roots for assessing belowground carbon allocation |
| VerfasserIn |
Jasper Bloemen, Bryan De Bel, Jonas Wittocx, Anne Thomas, Mary Anne McGuire, Robert O. Teskey, Kathy Steppe |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101540
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| Publikation (Nr.) |
 EGU/EGU2015-699.pdf |
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| Zusammenfassung |
| In trees, it is known that allocation of recent assimilates belowground fuels metabolic
processes like root respiration. Nonetheless, the fraction of carbon allocated belowground
remains poorly quantified as the energetic costs of tree root metabolism remain largely
unknown. Current estimates of root respiration are calculated from measurements of CO2
efflux from roots or soil. However, a substantial portion of CO2 released by root respiration
might remain within the tree root system rather than diffusing into the soil environment,
indicating that root respiration consumes substantially more carbohydrates than previously
recognized.
We measured internal CO2 concentration ([CO2]) and sap flow in three longitudinal
sections of two large roots of American beech (Fagus grandifolia) and yellow poplar
(Liriodendron tulipifera) trees (n=4 trees per species), while simultaneously measuring [CO2]
in neighboring soil. We hypothesized that [CO2] would be lowest in soil and increase from
the root tip to the base of the stem. We observed substantially higher [CO2] in tree roots (on
average 8.5 ± 2.0 and 5.2 ± 1.9 Vol% for American beech and yellow poplar, respectively)
compared with the soil environment (1.0 ± 0.4 and 1.3 ± 1.3 Vol% around American beech
and yellow poplar, respectively), indicating that root tissues exert substantial barriers
to outward diffusion of respired CO2. Moreover, we observed an internal [CO2]
gradient from root tip to stem base which suggests that progressively more respired
CO2 dissolved in flowing xylem sap as it moved from the soil through the root
xylem.
These results confirm that a fraction of root-respired CO2 concentrates in the xylem sap
of the root system and fluxes upward within the tree. This CO2 that is removed from the
site of respiration cannot be accounted for with measurements of CO2 efflux from
roots or soil, indicating that efflux-based techniques underestimate the energetic
costs of tree root metabolism and therefore the amount of carbon that is allocated
belowground. |
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