Wet fen meadows under traditional land use are nowadays mainly preserved through nature conservation measures. Recent discussions suggest that this land use may also be regarded as a form of paludiculture - that is, use of wet peatland with preservation of the peat body. However, the climate effect of this land use type is largely unknown. This study presents full two-year greenhouse gas (GHG) balances for two previously unexplored, long-term rewetted fens under a nature conservation management regime. Closed-chamber GHG fluxes were measured biweekly at two north-east German sites with acute sedge (Carex acuta) and at one site with creeping bentgrass (Agrostis stolonifera). Including harvest and dissolved carbon export, the CO2-eq emissions of the three sites were between 10.4 and 16.3 t ha(-1) yr(-1), with mean annual water levels between -10 and -19 cm relative to ground level. Emissions consisted mainly of CO(2 )uptake and release and were influenced by the timing and frequency of harvests as well as by periods of surface flooding during the growing season. CH4 emissions also contributed to the net GHG balances at two of the sites due to inundation in late summer 2014. N2O emissions were of minor importance at all three sites. This study shows that, with proper water management, the climate effect of fen meadows under management for nature conservation can be similar to that of other fen paludicultures, with a CO2-eq GHG mitigation potential of 15-20 t ha(-1) yr(-1) compared to drainage-based grassland use of fens. Therefore, for GHG reporting purposes, it may be justifiable to treat existing wet fen meadows under nature conservation management as paludicultures.

As the climate warms, winters with less snow and therefore more soil freeze-thaw cycles are likely to become more frequent in oceanic mountain areas. It is a concern that this might impair the soil's ability to store carbon and nutrients, and lead to increased leaching losses of dissolved C and nutrients and subsequent changes in nutrient cycling and ecosystem productivity. Through a combination of laboratory and field experiments, we studied short-term effects of changing winter conditions on carbon and nutrient leaching from two plant-soil systems with contrasting snow conditions (shallow/intermittent vs. deep/persistent snow). In the laboratory we exposed cores (soil and vegetation) from sites with either intermittent or persistent winter snow cover to five different freeze-thaw scenarios of realistic frequency and duration. Additionally, we set up a transplant experiment at our field site by reciprocally transplanting soil-plant monoliths between sites with intermittent and persistent snow. Together, the field and laboratory experiments aimed to assess how carbon and nutrient leaching was affected by both historical snow conditions and short-term (through freeze-thaw scenarios and transplantation) changes in snow cover and thermal conditions. Both a greater number of freeze-thaw cycles and longer duration of sub-zero temperatures increased carbon and nutrient leaching from incubated soil cores. Cores from sites with persistent snow generally had lower nutrient losses under control conditions, but greater losses following induced freeze-thaw cycles than cores from intermittent snow sites. The character of the leached dissolved organic carbon (DOC) suggested fresh organic material, such as live plant roots or microbes, as the source of carbon and nutrients. Nutrient losses from the plant-soil systems in the field were greater at sites with persistent winter snow due to greater volumes of percolating water in spring. This suggests that increasingly severe and frequent soil freeze-thaw events in oceanic mountain ecosystems can enhance the mobilization of C, N and P in labile forms but, in the absence of water fluxes, these nutrients would remain available for in-situ cycling. Thus, under future warmer winter conditions, increased carbon and nutrient losses from oceanic mountain ecosystems could occur if winters with little snow coincide with wet spring conditions.