Switch of fungal to bacterial degradation in natural, drained and rewetted oligotrophic peatlands reflected in δ15N and fatty acid composition

• Main Authors: Groß-Schmölders, Miriam, Sengbusch, Pascal, Krüger, Jan Paul, Woodard, Kristy, Birkholz, Axel, Leifeld, Jens, Alewell, Christine
• Format: Text
• Language: English
• Published: 2020
• Subjects: Northern Sweden
• Online Access: https://doi.org/10.5194/soil-2019-86; https://www.soil-discuss.net/soil-2019-86/

During the last centuries major parts of European peatlands were degraded along with drainage and land use changes. Peatland biodiversity and essential ecosystem functions (e.g. flood prevention, groundwater purification and CO 2 sink) were dramatically impaired. Moreover, climate change threatens peatlands in the near future. Increasing pressure to peatland ecosystems calls for a more cost-efficient method to indicate the current state of peatlands and the success of restoration effort. Metabolism processes in peatland soils are imprinted in stable isotope signatures due to differences in microorganism communities and their metabolic pathways. Therefore we hypothesize that depth profiles of nitrogen stable isotope values provide a promising opportunity to detect peatland decomposition or restoration. We studied five peatlands: Degerö Stormyr (Northern Sweden), Lakkasuo (Central Finland) and three mires in the Black Forest (Southern Germany). At all locations cores were taken from adjacent drained (or rewetted) and natural sites to identify δ 15 N trends that could indicate changes due to drainage and restoration. At all drained (and rewetted) sites we found a distinct peak (<q>turning point</q>) of the δ 15 N values in the center of the drained horizon. To verify our interpretation δ 13 C, the C / N ratio and the bulk density were measured and a microscopic analysis of the macro residuals in the peat cores was made. In addition we did a phospholipid fatty acid (PLFAs) analysis to link our results to microbial community composition. We distinguished between fungal and bacterial-derived PLFAs. In accordance with other studies, our results suggest, that fungi dominate the microbial metabolism in the upper, aerobic peat horizon. This is reflected by depleted δ 15 N values. Downwards the drained horizon conditions slowly switch to oxygen limitation. In consequence fungal-derived PLFAs decreases whereas bacterial-derived PLFAs are rising. The highest diversity of microbial-derived PLFAs is indicated by the δ 15 N turning point. Below the δ 15 N turning point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the onset of the permanently waterlogged, anaerobic horizon. Peatland cores with restoration success show, above the formerly drainage-affected horizon, again no depth trend of the isotopic values. Hence, we conclude that δ 15 N stable isotope values reflect microbial community composition, which differ between drained and natural peatlands.