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Peatlands contain 20-30 percent of the world's soil carbon stock. Because of drainage for agriculture and forestry resulting in peat oxidation, they currently emit large amounts of CO2. A promising alternative to drainage-based land use is paludiculture, i.e. agriculture and forestry on wet and rewetted peatlands with simultaneous peat formation or at least preservation of the peat body. Such new management practices involve using site-adapted (low ground pressure) machinery. The effects of machine mowing on the wet peatland ecosystem (biogeochemistry, carbon stocks) are poorly understood. Within the EU BiodivERsA project REPEAT (REstoration and prognosis of PEAT formation in fens - linking diversity in plant functional traits to soil biological and biogeochemical processes, 2017-2020), we have studied machine mown and unmown near-natural and restored wet percolation fens in the Netherlands, Germany, and Poland. We hypothesize that machine mowing in wet fens leads a) to a lower cover of potentially peat-forming plants, b) to a relocation (but no change) in overall below-ground biomass stocks, c) to higher bulk density and penetration resistance, and d) to a smaller decomposition rate of below-ground biomass. The hypotheses are largely based on knowledge from mineral soils and drained peat soils. Species composition has been studied by comparing vegetation relevés with regard to the occurrence of peat-forming species and functional groups. Below-ground biomass production in different depths has been assessed in ingrowth cores. Penetration resistance has been measured using a penetrologger. Decomposition rates have been assessed using litter bags with local root material and standard materials at different depths over 3 and 12 months. In a subset of sites, the long-term (>5 years) impact of a light tractor with wide tyres compared to a heavy tracked machine has been assessed, and additional properties (e.g. root porosity) were included. Here, also a before-after passage experiment was performed with the tracked machine. Knowledge about alterations of peat and vegetation due to machine mowing is crucial from a conservation point of view as well as for understanding peat formation and assessing restoration effects. The results have implications for the emerging field of paludiculture, where traffic for harvesting is a critical issue. [ABSTRACT FROM AUTHOR]

Peatland degradation is tightly connected to hydrological changes and microbial metabolism. To better understand these metabolism processes, more information is needed on how microbial communities and substrate cycling are affected by changing hydrological regimes. These activities should be imprinted in stable isotope bulk values (δ 15 N, δ 13 C) due to specific isotopic fractionation by different microbial communities, their metabolic pathways and nutrient sources. We hypothesize that stable isotope values and microbial abundance are correlated and act as indicators of different hydrological regimes. We sampled an East-West transect across European fens in 14 areas and conducted a stable isotope (δ 13 C, δ 15 N) and membrane fatty acid (mFA) analysis. Within each area an undrained, drained and rewetted site was selected. Rewetted sites were separated based on when rewetting occurred. We found differences in the upper layers of all sites in microbial-derived mFAs and stable isotope values corresponding to hydrological regimes. The highest and lowest quantities of microbial-derived mFAs were measured in undrained and drained sites, respectively. Fungal-derived mFAs were especially lower in drained sites. Simultaneously, δ 15 N stable isotope values were highest in drained sites. In addition, stable isotope values and microbial-derived mFAs showed distinct depth trends. In undrained sites stable isotopes values slightly increased with depth. In drained sites, δ 15 N values decreased downwards, whereas δ 13 C values increased. Overall microbial-derived mFAs decreased with depth. These patterns presumably result from anoxic conditions and high peat recalcitrance in the deeper layers. In sites with short time of rewetting, the microbial-derived mFAs and stable isotope values were similar to values of drained sites, while with increasing rewetting time values shifted to those of undrained sites. We conclude that biomarkers indicate that stable isotope values reflect specific microbial metabolic processes, which differ with hydrological regimes, and thus could indicate both drainage and rewetting in fens., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2022. Published by Elsevier B.V.)

In peatland restoration we often lack an information whether re-established ecosystems are functionally similar to non-degraded ones. We re-analysed the long-term outcomes of restoration on vegetation and plant functional traits in 38 European fens restored by rewetting (18 sites) and topsoil removal (20 sites). We used traits related to nutrient acquisition strategies, competitiveness, seed traits, and used single- and multi-trait metrics. A separate set of vegetation records from near-natural fens with diverse plant communities was used to generate reference values to aid the comparisons. We found that both restoration methods enhanced the similarity of species composition to non-degraded systems but trait analysis revealed differences between the two approaches. Traits linked to nutrient acquisition strategies indicated that topsoil removal was more effective than rewetting. After topsoil removal competitive species in plant communities had decreased, while stress-tolerant species had increased. A substantial reduction in nutrient availability ruled out the effect of initial disturbance. An ability to survive and grow in anoxic conditions was enhanced after restoration, but the reference values were not achieved. Rewetting was more effective than topsoil removal in restricting variation in traits values permitted in re-developing vegetation. We found no indication of a shift towards reference in seed traits, which suggested that dispersal constraint and colonization deficit can be a widespread phenomena. Two functional diversity indices: functional richness and functional dispersion showed response to restoration and shifted values towards reference mires and away from the degraded systems. We concluded that targeting only one type of environmental stressor does not lead to a recovery of fens, as it provides insufficient level of stress to restore a functional ecosystem. In general, restoration efforts do not ensure the re-establishment and long-term persistence of fens. Restoration efforts result in recovery of fen ecosystems, confirmed with our functional trait analysis, although more rigid actions are needed for restoring fully functional mires, by achieving high and constant levels of anoxia and nutrient stresses., Competing Interests: The authors have declared that no competing interests exist.