Switch of fungal to bacterial degradation in natural, drained and rewetted oligotrophic peatlands reflected in δ<sup>15</sup>N and fatty acid composition

Abstract

Abstract. 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 CO2 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 δ15N trends that could indicate changes due to drainage and restoration. At all drained (and rewetted) sites we found a distinct peak (turning point) of the δ15N values in the center of the drained horizon. To verify our interpretation δ13C, 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 δ15N 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 δ15N turning point. Below the δ15N 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 δ15N stable isotope values reflect microbial community composition, which differ between drained and natural peatlands.

The Kulbäcksliden Research Infrastructure: a unique setting for northern peatland studies

“…Microclimate and microtopography control plant (Wiedermann and Nilsson, 2020) and microbial community composition (Økland, 1990;Robroek et al, 2014). Consequently, changes in the local conditions could induce substantial changes in the abundance and activity of microorganisms as observed for the altered activity of methanogens with increased temperature, N and S (Martí et al, 2015; or the dominance of fungal or bacterial activity depending on the management regime of peatlands (Groß-Schmölders et al, 2020). Increased vascular plant disease occurrence due to parasitic fungi has been observed with increased N deposition which may have important implications for CO 2 and CH 4 exchange between mires and the atmosphere (Wiedermann et al, 2007).…”

Electron Accepting Capacities of a Wide Variety of Peat Materials From Around the Globe Similarly Explain CO2 and CH4 Formation

“…Interestingly, the available range of EAC OM in our study was unrelated to any of the investigated peat quality indices except for a weak correlation with values of δ 13 C and δ 15 N, possibly related to pathways of decomposition (Drollinger et al., 2019; Groß‐Schmölders et al., 2020; Teickner et al., 2022). While existing studies (Aeschbacher et al., 2010, 2011, 2012) reported a positive correlation with indices representing the aromaticity of the sample, we could not confirm such a relationship.…”

“…The same holds true in our sample set: N/P ratios were on average 37.2 ± 15.4 (no difference between bogs and fens). Lowest, partly negative δ 15 N values were reported for peat material being long‐term under aerobic decomposition, whereas higher, positive values were found in layers with predominantly anaerobic decomposition (Groß‐Schmölders et al., 2020). Again, in our data set, lower depth classes showed high δ 15 N values and N enrichment due to intense recycling during decomposition, for example, in initial fen stages (Jones et al., 2010).…”

“…Furthermore, the mass ratio of N/P may serve as a valuable proxy to determine the nutritional status of the peat (Wang et al., 2015). Moreover, values of δ 13 C and δ 15 N have been proposed to serve as indicators of decomposition (Alewell et al., 2011; Biester et al., 2014; Groß‐Schmölders et al., 2020).…”