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| Titel |
Enhanced photosynthetic efficiency in trees world-wide by rising atmospheric CO2 levels |
| VerfasserIn |
Ina Ehlers, Thomas Wieloch, Peter Groenendijk, Mart Vlam, Peter van der Sleen, Pieter A. Zuidema, Iain Robertson, Jurgen Schleucher |
| 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 |
250097046
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| Publikation (Nr.) |
 EGU/EGU2014-12587.pdf |
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| Zusammenfassung |
| The atmospheric CO2 concentration is increasing rapidly due to anthropogenic emissions but
the effect on the Earth’s biosphere is poorly understood. The ability of the biosphere to fix
CO2 through photosynthesis will determine future atmospheric CO2 concentrations as well as
future productivity of crops and forests. Manipulative CO2 enrichment experiments (e.g.
FACE) are limited to (i) short time spans, (ii) few locations and (iii) large step increases in
[CO2]. Here, we apply new stable isotope methodology to tree-ring archives, to study the
effect of increasing CO2 concentrations retrospectively during the past centuries. We
cover the whole [CO2] increase since industrialization, and sample trees with global
distribution.
Instead of isotope ratios of whole molecules, we use intramolecular isotope distributions,
a new tool for tree-ring analysis with decisive advantages. In experiments on annual plants,
we have found that the intramolecular distribution of deuterium (equivalent to ratios of
isotopomer abundances) in photosynthetic glucose depends on growth [CO2] and reflects the
metabolic flux ratio of photosynthesis to photorespiration. By applying this isotopomer
methodology to trees from Oak Ridge FACE experiment, we show that this CO2 response is
present in trees on the leaf level. This CO2 dependence constitutes a physiological signal,
which is transferred to the wood of the tree rings.
In trees from 13 locations on all continents the isotopomer ratio of tree-ring cellulose is
correlated to atmospheric [CO2] during the past 200 years. The shift of the isotopomer ratio is
universal for all 12 species analyzed, including both broad-leafed trees and conifers. Because
the trees originate from sites with widely differing D/H ratios of precipitation, the generality
of the response demonstrates that the signal is independent of the source isotope ratio,
because it is encoded in an isotopomer abundance ratio. This decoupling of climate signals
and physiological signals is a fundamental advantage of isotopomer ratios (Augusti et al.,
Chem. Geol 2008).
These results demonstrate that increasing [CO2] has reduced the ratio of photorespiration
to photosynthesis on a global scale. Photorespiration is a side reaction that decreases the C
gain of plants; the suppression of photorespiration in all analyzed trees indicates that
increasing atmospheric [CO2] is enhancing the photosynthetic efficiency of trees
world-wide.
The consensus response of the trees agrees with the response of annual plants in
greenhouse experiments, with three important conclusions. First, the generality of the
isotopomer shift confirms that the CO2 response reflects the ratio of photosynthesis to
photorespiration, and that it creates a robust signal in tree rings. Second, the agreement
between greenhouse-grown plants and trees indicates that there has not been an acclimation
response of the trees during the past centuries. Third, the results show that the regulation of
tree gas exchange has during past centuries been governed by the same rules as observed in
manipulative experiments, in contradiction to recent reports (Keenan et al., Nature 2013). |
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