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| Titel |
Effects of seasonality and girdling on the age of stem CO2 in mature tropical lowland forest trees (Scleronema micranthum) |
| VerfasserIn |
Jan Muhr, Norbert Kunert, Alon Angert, Niro Higuchi, Susan E. Trumbore |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099552
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| Publikation (Nr.) |
 EGU/EGU2014-15346.pdf |
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| Zusammenfassung |
| Little is known about the use of carbon (C) that was assimilated more than 1 year previously
in trees. As a tree’s lifetime is measured in decades to centuries, and trees are known to be
able to build up essential nonstructural C reserves, it is possible that years elapse between
fixation and later metabolic return of C to the atmosphere. We will refer to this elapsed time
here as the “age” of CO2, and we measure it by comparing the radiocarbon (14C)
signature of CO2 emitted by trees with the observed rate of decline in atmospheric
14C-CO2.
Here, we report data from Scleronema micranthum trees from a tropical lowland forest
near Manaus, Brazil. Starting with 7 trees in 2012, we looked for seasonal changes in the age
of CO2 emitted from the tree stem surface into the surrounding atmosphere as well as CO2
extracted from several depths (4, 8, and 12 cm) within the tree stem. We found no clear
seasonality, but instead found that almost all samples were influenced by CO2 originating
from sources fixed up to several years previously, suggesting that trees make use of storage C
pools on a regular basis. There was a clear pattern of CO2 samples getting older the deeper
from the stem they were extracted. The oldest samples, extracted from 12 cm depth, were
made up of C fixed up to 30 years previously in some cases. The CO2 that is emitted
into the atmosphere at the stem surface presumably represents a mixture of CO2
produced at various depths within the stem, and hence on average was substantially
younger than these old samples, but still had an average age between 0-6 years.
These findings of trees regularly using previously fixed C contradict the widespread
assumption that trees mainly rely on recent assimilates for respiration unless forced to
mobilize C from older pools due to environmental conditions limiting assimilation
rates.
In April 2013, we increased the number of investigated trees from 7 to 12. Initially,
we kept the original sampling design, measuring seasonal CO2 ages twice for all
trees, before – in October 2013 – we finally girdled half of the trees to investigate
how completely cutting off the supply of recently assimilated C from the leaves
to the stem affects the age of respired CO2 in the girdled trees compared to the
ungirdled control. Initially, we hypothesize an increase of the age of respired CO2 in the
beginning, due to a mobilization of older storage C. It is unclear however, how long
this increase can be observed, or what the maximum age of observed emissions
could be, as such an experiment has not yet been carried out to our knowledge. |
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