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| Titel |
Redox processes in the rhizosphere of restored peatlands - The impact of vascular plant species on electrochemical properties of dissolved organic matter |
| VerfasserIn |
Svenja Agethen, Franziska Wolff, Klaus-Holger Knorr |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135475
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| Publikation (Nr.) |
 EGU/EGU2016-16346.pdf |
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| Zusammenfassung |
| Restoration of cut over peatlands in Central Europe is challenging in a landscape overused for
agriculture. Excess nutrient availability by excess fertilization triggers uncharacteristic
vegetation that is one key driver for carbon cycling. Those nutrient rich systems are often
dominated by graminoids, and were often found to emit substantial amounts of methane.
Plants grown under nutrient rich conditions provide more labile carbon in rhizodeposition and
litter that fuels methanogenesis. Such species often have aerenchyma that facilitates
direct CH4 emissions to the atmosphere and therefore impair the climate cooling
function of bogs. On the other hand, aerenchymatic tissue supplies oxygen to the
rhizosphere, which may reduce methanogenesis or stimulate methane oxidation, as
methanogenesis is a strictly anaerobic process. Which of the effects prevail is often
unclear.
Therefore, the aim of this study was to test the impact of different vegetation on
rhizospheric redox conditions and methanogenesis, including aerenchymatic vascular plants
that are dominant in restored cut over peatlands. As ombrotrophic peat is poor in inorganic
electron acceptors (EAs) to suppress methanogenesis, we analyzed the electron acceptor
(EACs) and electron donor capacities (EDCs) of dissolved organic matter (DOM) in the
rhizosphere to understand the impact of vegetation on anaerobic organic matter
degradation.
We planted Juncus effusus, Eriophorum vaginatum, Eriophorum angustifolium,
Sphagnum (mixture of S. magellanicum, S. papillosum, S. sec. acutifolia, 1/3 each) plus
non-vegetated controls; six replicates per batch; in containers with untreated homogenized
peat. The plants grow under constant conditions (20˚ C, 12h diurnal light cycles and 80%
RH). Anoxic conditions were achieved by keeping the water table at +10 cm. For monitoring,
the rhizosphere is equipped with suction and gas samplers. We measure dissolved
CO2 and CH4 concentrations, inorganic EAs (NO3−, Fe(III), and SO42−) and
organic EDCs and EACs via mediated electrochemical reduction/oxidation. We
also characterize DOM with fluorescence spectroscopy and monitor the growth of
above ground biomass as proxy for photosynthetic activity and potential DOM
source.
Preliminary results showed after initially equal magnitude of EACs and EDCs in all
batches an increase in total electron exchange capacity (Σ EAC, EDC) four weeks later,
but EACs increased significantly higher for rooted plants (fivefold vs. threefold in
Sphagnum and controls). Subsequently, higher CH4 concentrations were found
for Sphagnum and the controls. In our ongoing study we will also try to relate the
effect of vegetation on rhizosphere redox conditions to root and shoot biomass and
photosynthesis.
First results indicate that oxidation of organic EAs occurs for all tested graminoid
species. The analysis of EACs and EDCs in the rhizosphere of dominant species
may improve our understanding under which conditions methane production and
emission is stimulated or reduced by presence of vascular, aerenchymatic plants. |
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