Microbial cycling of iron in acidic fens
Final Report Abstract
In the light of increasing extreme weather conditions in Europe as predicted due to climate change, this study aimed at investigating minalization processes under extreme drought and heavy rainfall events in a minerotrophic fen. The studied processes included effects on the activity of exoenzymes, CO2 and CH4 formation as well as Fe(II)-reduction in a field based manipulation experiment. We could show that the drying and rewetting of fen soil did not eliminate the critical mechanisms restricting the re-release of CO2 which was predicted by the enzymic latch hypothesis. The mineralisation processes in the fen were not enhanced since the upper most active fen soil layer were already adjusted to water table changes. The pathways of CH4 were not altered and we could show that acetate is the main precursor of CH4 in the upper fen soil layers and that a shift to H2 as main substrate occurs in deeper soil layers. Pathways of acetate as important intermediate in C-cycling were investigated together with the acetogenic community. The drying and rewetting shifted the flow of reductants from organic matter decomposition away from methanogenesis towards other anaerobic processes like nitrate, Fe(III) and sulphate reduction and prolonged the phase of Fe(III) reduction. We conclude that the impact of more frequent extreme weather conditions on peatlands comparable to the invested fen Schlöppnerbrunnen will not contribute to further CO2 release as the soil has almost no potential for further degradation due to low usable C in deeper soil layers. We also established a peat quality factor that can help estimating the potential greenhouse gas formation of peat soil. As the site is especially rich in iron, we illuminated the microbial cycling of iron and could show that Fe(II) oxidizer occur together with Fe(III) reducer which facilitates Fe-cycling close to the anoxic-oxic boundary situated in 10-20 cm peat soil depth. We successfully isolated a Fe(II) oxidizer strain CL21 closely related to Sideroxydans lithotrophicus and assessed the community composition of both Fe(II) oxidizers as well as Fe(III) reducers. Fe-minerals present at the site and the influence of the humic acids in peat soil on Fecycling are further investigated.
Publications
- (2008): Competition of Fe(III) reduction and methanogenesis in an acidic fen. FEMS Microbiology Ecology 65: 88-101
Reiche, M., Torborg, G. and Küsel, K.
- (2008): Microbial reduction of iron and porewater biogeochemistry in acidic peatlands. Biogeosciences 5: 1537-1549
Küsel, K., Blöthe, M., Schulz, D., Reiche, M., Drake, H.L.
- (2009): Impact of manipulated drought and heavy rainfall events on peat mineralization processes and source-sink functions of an acidic fen. J. Geophys. Res.-Bio. 114
Reiche, M., Hädrich, A., Liescheid, G., and Küsel, K.
(See online at https://doi.org/10.1029/2008JG000853) - (2010): Acid-tolerant microaerophilic Fe(II)-oxidizing bacteria promote Fe(III)-accumulation in a fen. Environmental Microbiology 12 (10): 2814–2825
Lüdecke, C., Reiche, M., Eusterhues, K., Nietzsche, S., Küsel, K.
- (2010): Effect of peat quality on microbial greenhouse gas formation in an acidic fen. Biogeosciences 7: 187-198
Reiche, M., Gleixner, G., Küsel, K.
