Plant diversity controls biogeochemical peat properties within an ombrotrophic bog in Southern Patagonia

Regina Anzenhofer1, Werner Borken2, Klaus-Holger Knorr3
1 Dept. of Hydrology, Limnological Research Station, University of Bayreuth
2 Dept. of Soil Ecology, University of Bayreuth
3 ILÖK, Hydrology Group, University of Münster

O 6.3 in Biogeochemistry of wetlands

15.07.2014, 11:40-12:00, H17

Peatlands have been studied as environmental archives for e.g. climate or hydrological conditions, based on the fact that peat decomposition is largely determined by hydrology and climate. Changes in vegetation and thus changes in the quality of carbon inputs may, however, modify signals in the decomposition records. Moreover, the evolution of a peatland may involve the formation of in-site variability in moisture and vegetation, e.g. hummocks, lawns, and medium scale surface topography. As such features are not constant in space and time, a peat profile reflects both regional climatic and hydrological information and local, micro-site specific modifications of those signals.

In order to understand within-site variability, we investigated a moisture and vegetation gradient along a 650 m transect in an oceanic, ombrotrophic bog in Southern Patagonia. Along the transect, the conditions changed from a wet, Sphagnum dominated site (Sphagnum magellanicum), intermediate drier and wetter sites with sphagnum/shrubs mixtures (Gaultheria Antarctica, Empetrum rubrum),sedges and rushes (Tetroncium magellanicum, Carpha spp. Marsippospermum grandiflorum), to drier, more wind exposed sites, dominated by cushion plants (Oreobolusobtusangulus, Astelia pumila, Donatia fascicularis). We hypothesized that under arenchymatic cushion plants and under plant supplying more labile carbon, carbon turnover is greatly enhanced.

Investigations along the transect demonstrated high variability of depth records within the bog. The profile at the Sphagnum dominated site had a D14C of -430 per mil (age of 4450 y) at 270 cm depth, while for the cushion plant dominated site a D14C of -680 per mil (age of 9100 y) was measured at the same depth. Peat accumulation under Sphagnum was thus considerably higher during the past millennia. Accordingly, the peat under cushion plants was much more decomposed, with C/N ratios of 20-50 compared to C/N ratios of 40-80 under Sphagnum patches. Mixed sites in between had C/N ratios of 30-90, depending on plant community. Humification indices as obtained from FTIR spectra tended to be lower at the Sphagnum sites. In the liquid phase, concentrations of DOC were higher under Sphagnum and also here, fluorescence spectra of DOC revealed higher contribution of protein-like fluorescence, which was close to zero at the cushion plant sites. Furthermore, the fluorescence index of samples suggested higher contribution of microbially processed DOC at the cushion plant sites and higher contribution of plant derived DOC at the Sphagnum site.

Our study supports that peat decomposition processes are largely controlled by plant diversity. Presence of aerenchymatic cushion plants lead to a decrease in the concentration of labile carbon compounds in the pore water, to highly decomposed peat and less peat accumulation. For sites with gradients in hydrology and vegetation, spatio-temporal changes in carbon turnover and accumulation have thus to be considered.

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Letzte Änderung 03.04.2014