CONTEXT Humanity must overcome the polycrisis of biodiversity loss, climate change and pollution. These challenges are especially urgent in peatlands, which develop slowly under waterlogged conditions, function as landscape filters and store large amounts of carbon. Drainage for agriculture, forestry or peat extraction leads to severe socio-ecological impacts, including greenhouse gas emissions, biodiversity loss, land subsidence, higher flood and drought risks and downstream pollution. OBJECTIVE This study evaluates paludiculture as an innovative wet agricultural land use that maintains wet peatlands, offers economic alternatives to drainage-based systems and reduces environmental impacts. METHODS We reviewed and synthesized ecological and socio-economic evidence from low- and high intensity paludiculture practices to assess their potential to balance human needs with peatland conservation. RESULTS AND CONCLUSIONS Paludiculture is a promising new agricultural land use that effectively reduces greenhouse gas emissions, supports biodiversity restoration and contributes to climate mitigation and sustainable development. Our findings show direct and indirect contributions to ten UN Sustainable Development Goals: no poverty, good health, clean water, clean energy, innovation, sustainable cities and communities, responsible production, climate action, life below water, and life on land. Nonetheless, challenges remain regarding economic viability, land-use competition and management. SIGNIFICANCE Paludiculture shows how wetland agriculture can create new revenue opportunities combined with ecological protection. By contributing to both climate and biodiversity goals, it is a sustainable alternative to drainage-based peatland use.

Approximately half of Europe's peatlands have been extensively drained for agriculture, forestry, and peat extraction, with lowland fens disproportionately affected due to their high nutrient availability and productivity post-drainage. Peatland rewetting has gained importance as a strategy to mitigate carbon losses and restore biodiversity; however, its effectiveness in reestablishing below-ground processes remains uncertain. Soil organic matter (SOM) dynamics play a crucial role in peatland restoration outcomes, influencing peat structural integrity and hydrological properties, as well as the availability of substrates and nutrients for microbial and plant communities. Here, we present a Europe-wide assessment of the effects of fen drainage and rewetting on SOM molecular composition, analyzing fens with contrasting hydrological status (undrained, drained, and rewetted) across three depths (0 - 5, 15 - 20, and 45 - 50 cm) using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Despite considerable variability induced by site-specific heterogeneity, the molecular composition of undrained fens clearly reflected the dominant contributions of sedges, grasses, and brown mosses to peat formation in fens, with characteristic stratification. Drainage consistently led to a decline in components from plant biopolymers (carbohydrates and lignins) across sites, and an increase in microbially altered compounds (Ncompounds, benzenes, and aliphatics), with the most pronounced effects at intermediate depths (15 - 20 cm). Rewetting partially reversed these alterations, with some fens exhibiting a shift in molecular composition reverting toward undrained conditions, particularly in sites rewetted for longer periods. However, significant differences remained between rewetted and undrained fens. Our findings suggest that while rewetting over time can facilitate partial recovery of carbon dynamics, the below-ground legacy of drainage-induced alterations can persist, at least for a timescale of several decades.

Rewetting drained peatlands can lead to high nutrient mobilization, increased methane emissions, and a slow re-establishment of peat-forming vegetation. To guide effective restoration and management, understanding the temporal and spatial variability in porewater chemistry is essential. This study surveyed 64 natural and rewetted peatlands across Germany, Poland, Estonia, Sweden, Georgia, and Scotland from 1997 to 2017. A total of 812 anoxic porewater samples were collected using dialysis samplers (0-0.6 m depth). The rewetted fens exhibited a wide range of dissolved substances, spanning orders of magnitude for soluble reactive phosphorus (SRP: 0.1-18.9 mg L-1), ammonium (NH4+-N: 0.1-117.3 mg L-1), and dissolved organic carbon (DOC: 13-313 mg L-1). However, the mean concentrations were significantly higher than those observed in natural fens (p < 0.05). Depth-integrated mobilization rates for nutrients in rewetted fens were, on average, 23 times higher for SRP (1.8 mg P m(-2) d(-1)) and 4.6 times higher for NH4+-N (3.6 mg N m(-2) d(-1)) compared to their natural counterparts (0.1 mg P m(-2) d(-1) and 0.8 mg N m(-2) d(-1)). Seasonal variation was also evident in rewetted fens densely colonized by helophytes, with SRP concentrations being lower in the growing season. Notably, SRP concentrations remained elevated 10-20 years after rewetting; however, a 50-80 % decrease was observed at sites characterized by comparatively low iron content in the peat (< 20 mg g(-1) dry mass). Further investigations should explore how nutrient dynamics evolve over extended rewetting periods in different contexts, including climate change.

Introduction:Fens, unlike bogs, are mires fed by ground or surface water, usually enriched by minerals and nutrients, which allows them to support high and specific biodiversity. Fens are dominant mires of the more continental temperate areas and the Arctic but they are also common in some of the boreal regions. Even though much less recognized than bogs, they remain globally important carbon stores and sinks. Their major peat builders are sedges and so-called brown mosses (non-Sphagnum bryophytes) which have been much less studied in the context of biomass quality than Sphagnum species. In the presented study we aimed to quantify the biomass quality (decomposability) of the common fen bryophytes along more than 15 degrees south-to-north transect.Material and methodsWe studied the biomass quality of fen bryophytes in three regions: temperate fens of NE Poland, mid-boreal Trøndelag, and sub-arctic Finnmarksvidda (both latter in Norway). Studied species were Campyllium stellatum, Scorpidium cossonii, Sphagnum warnstorfii and Tomentypum nitens. In each region, mosses were collected from several sites during the summer of 2022. Each collected moss sample was divided into two. One was quickly dried and the latter was kept alive and later grown in a common garden in standardized conditions, for more than a month, to produce new biomass. Both the biomass collected in the field and the new biomass produced in the common garden experiment were analysed with NIR spectroscopy to assess their biomass quality. We compared the impact of origin on biomass quality of both original biomass and the one produced in common conditions using mixed effect models with location and species as the random factors.ConclusionsThe obtained results shed light on the possible impacts of climate warming on peat formation in fens. Assuming that fens will maintain their integrity in the course of climate change, this change may impact the peat-forming potential of fens via changes in bryophyte community composition as well as by impacting the performance and biomass quality of the locally occurring species. Thus studying bryophyte biomass quality along the climatic gradient might help us to better predict the future of carbon accumulation in fens.

Abstract. This study investigated whether rewetting of drained temperate, groundwater-fed fens results in consistent shifts of above- and belowground production and litter mass loss of vascular plants, as compared to undrained fens, and how these processes relate to abiotic and biotic factors. We tested the hypotheses that (1) due to higher availability nutrient rewetted and drained fens exhibit higher production, (2) due to higher decomposability of plant biomass rewetted fens show higher plant biomass decomposition than undrained, and (3) in rewetted fens, less peat is potentially formed than in undrained fens. We analysed the effects of hydrological status (undrained, drained, rewetted) on plant production and litter mass loss during one year in 39 peatland sites across temperate Europe. Above- and belowground productivity, as well as mass loss of autochthonous vascular plant litter and Rooibos tea were measured above- and belowground. Aboveground vascular plant production was higher in rewetted fens than in undrained fens, in line with our first hypothesis. This difference was linked to the proportional graminoid cover and N content in aboveground biomass. In contrast to our first hypothesis, belowground production did not differ between fens of different hydrological status. It was highest in the 0–5 cm horizon, where soil temperature, and microbial biomass were also highest. Likewise, and in contrast to our second hypothesis, decomposition of above- and belowground vascular plant biomass was not affected by hydrological status. Only Rooibos tea mass loss showed small, ecologically irrelevant differences between differing hydrological statuses. Decomposition of aboveground biomass at soil surface was higher with higher nitrogen and phosphor content of the biomass, higher soil temperature, and higher cover proportion of herbs in the vegetation. Belowground biomass loss was positively correlated with phosphor content in soil porewater and aboveground biomass. One-third of the overall belowground biomass production took place in the 0–5 cm horizon, while decomposition in this horizon was lower than in the subsoil, irrespective of hydrological status. Our third hypothesis was also not confirmed because belowground production, decomposition and peat formation potential did not differ between the hydrological status. Although aboveground vascular plant production was higher in rewetted fens higher than in undrained, this difference will not result in a higher peat formation potential in rewetted fens due to the strong decomposition in of the easily degradable aboveground vascular plant biomass on a long time. Rather than hydrological status, soil depth, and nitrogen and phosphor availability had stronger impact on short-term vascular plant production and mass loss in the temperate fens studied. All these results were obtained during an extremely dry and warm growing season throughout Europe and causing deep drop downs of the water level at most sites. These meteorological conditions may have impacted the observed pattern of productivity and decomposition in unknown way.

Palsa mires constitute a zonal peatland type in the discontinuous permafrost region of the Northern Hemisphere. They typically consist of permafrost mounds and thermokarst ponds. Global warming has accelerated thawing of permafrost in palsa mounds and an increase in the area of thermokarst ponds in recent decades. Understanding long-term consequences of this process requires in-depth knowledge of the internal diversity of palsa mire vegetation types and their functions. Most studies so-far focused on the palsa mounds. Hereby, we focus on the thermokarst ponds, analysing their vegetation composition and habitat conditions from the top of a palsa plateau down to a fen without current palsa formation close to an adjacent river. We observed a distinct ecological gradient from Sphagnum-dominated ponds in the uppermost part of peat plateau to brown moss-dominated fen flarks at the riverside. This reflected well the poor - rich gradient typically recognised in mire vegetation, confirmed by our hydrochemical analyses. However, in contrast to the gradual shifts in species composition along typical mire zonation in temperate regions, palsa microtopography with mounds, rims, strings, and hollows, creates a sequence of mire basins forming a discrete gradient from base-poor to base-rich conditions, allowing different plant species to dominate these distinct locations.

Abrupt global warming poses threats to hydrological cycles and peatland ecosystem development. Northern peatlands, such as palsa mires, experience prompt degradation due to disappearing ice cores caused by increasing air temperatures and changes in precipitation patterns that induce the development of thicker snow covers insulating existing ice cores that impair their development. Disappearing palsa mires are experiencing subsidence, which in turn is flattening their topography and changing their hydration. What's more, changes in the shape and position of the ice cores cause local changes in water flow, and the lowering surface of the peatlands approaches the groundwater table, increasing their saturation. Increasing the moisture content of the topsoil within the degrading palsa mire system, in turn, causes changes in biogeochemical processes manifested in changes in water balance, carbon balance, and plant species composition. It, therefore, seems that the ongoing decomposition of palsa mires results in the development of novel peatland ecosystems, which, despite not being affected by the thermokarst processes, are suspected to become effective carbon sinks capable to sequestrate massive amounts of carbon that, in turn, may decrease greenhouse gas emissions. We conducted a comprehensive field-research-based study on Šuoššjávri palsa mire located in Northern Norway (Finnmark). We documented the water balance of the peatland. We described the structure of the palsa mire with the use of electrical resistivity imaging. We modeled the directions of groundwater flow. We applied an Interferometric Satellite Radar approach to quantify the speed of peatland subsidence. We used automated chambers to measure greenhouse gas emissions in a gradient of palsa peatland deterioration and a thermokarst lake. We also applied a novel approach to document vertical profiles of dCO2 and dCH4 content in groundwater at different levels of the peatland with the use of newly developed piezometers to check whether palsa-deterioration-driven groundwater flow patterns can affect carbon sequestration. We documented that subsidence of palsa peatland occurs at a rate of about 2 mm/year while peatlands formed in place of disappearing palsa peatland grow steadily, most likely due to the persistence of stable moisture content and the maintenance of a proper peat-forming process. We revealed that the degradation of palsa mire can be expressed by a range of hydrological indicators representing the duration of groundwater levels at specific depths: inundation time at matured peatlands that remain one of the last steps of palsa mire degradation is shortening, which, in turn, results in limiting methane emissions, yet keeping the carbon dioxide emissions at levels twice as low as the ones documented in a thermokarst lake. Botanical analyses allowed us to describe the development of peatlands that formed in the place of degraded palsa mires and to quantify biomass production and peat accumulation. In the light of results of our study, we hypothesize that degradation of palsa peatlands due to climatic change results in the development of peatland ecosystems that are likely to prevent global warming due to stable and high topsoil saturation followed by an efficient carbon sequestration in the peat-forming process and novel peatland development.

Drainage for agriculture has transformed temperate fen peatlands from carbon sinks into major carbon sources. Rewetting can halt this degradation, and the productive use of rewetted peatlands through paludiculture offers a promising sustainable land use strategy. However, historical drainage increases nutrient availability, which often remains elevated after rewetting. It is unknown how such nutrient conditions affect the potential of rewetted peatlands to form new peat, particularly under paludiculture use. We studied rewetted fens across temperate Europe with varying land uses (no use, low- and high-intensity paludiculture) and nutrient availability (low in Carex-dominated sites, high in Typha-dominated sites and quantified by Ellenberg Indicator Values). Over 2 years, we measured belowground biomass production using root ingrowth cores and decomposition using litterbags and calculated the peat formation potential as the standardized balance between these two processes. We hypothesized that paludiculture does not reduce peat formation potential compared to no agricultural land use after rewetting, that nutrient enrichment affects both production and decomposition equally, and that water availability and nutrient levels are key drivers of these processes. Paludiculture did not negatively affect peat formation potential in rewetted fens compared to non-used sites. Unexpectedly, belowground biomass production was higher in low-nutrient Carex-dominated sites than in high-nutrient Typha-dominated sites, while decomposition rates showed little difference across vegetation types and were lowest below moderate nutrient availability. Peat formation potential increased with a longer growing season, high water levels, and low nutrient availability. This is the first field-based study to quantify the balance of production and decomposition under different management and nutrient regimes in rewetted fens. The findings support the use of paludiculture on degraded, nutrient-rich fens to reduce nutrient loads and steering them to high peat formation potential, offering a sustainable solution for peatland restoration and agricultural land use.

Understanding whether nitrogen (N), phosphorus (P) or potassium (K) (co)limit productivity across biodiverse herbaceous habitats is crucial to guide management. Therefore, we investigated for 386 plots representing 13 nutrient-limited habitat types across Europe whether community N:P:K stoichiometry and limitation types differ along wide-ranging gradients in soil development, moisture and pH. Results indicate P/P+N as frequent as N limitation. K/K+N limitation occurs not where K availability is minimal, but in species-impoverished habitats with excess N and P. Overall, P emerges as primary driver of stoichiometry, strongly driven by the environment: at optimal pH of 6, N:P and P/P+N limitation are minimal and N limitation maximal, despite also good conditions for N availability. At pH<5 and >7, N:P is high and P/P+N limitation common. Our findings emphasize soil pH control on nutrient limitation through influence on P. Studies reporting widespread K (co)limitation in temperate herbaceous vegetation likely sampled anthropogenically P/N-enriched communities. ### Competing Interest Statement The authors have declared no competing interest.

The EU Nature Restoration Law (NRL) is critical for the restoration of degraded ecosystems and active afforestation of degraded peatlands has been suggested as a restoration measure under the NRL. Here, we discuss the current state of scientific evidence on the climate mitigation effects of peatlands under forestry. Afforestation of drained peatlands without restoring their hydrology does not fully restore ecosystem functions. Evidence on long-term climate benefits is lacking and it is unclear whether CO2 sequestration of forest on drained peatland can offset the carbon loss from the peat over the long-term. While afforestation may offer short-term gains in certain cases, it compromises the sustainability of peatland carbon storage. Thus, active afforestation of drained peatlands is not a viable option for climate mitigation under the EU Nature Restoration Law and might even impede future rewetting/restoration efforts. Instead, restoring hydrological conditions through rewetting is crucial for effective peatland restoration.

Introduction:A reliable method for measuring brown moss production helps us to understand the functioning of fen peatlands and to quantify their peat formation rate. However, traditional methods based on height increment are not suitable for measuring the growth rate of brown mosses with numerous lateral branches.Methods:The growth rate of common brown moss species in temperate and boreal fens was measured using two methods: (i) the marking method - a moss shoot was marked with oil paint and its growth increment measured from the mark (in the laboratory and in the field); and (ii) the plug method - a fragment of a moss colony was 'plugged' (i.e. cored), weighed and replanted in a small basket for a year, then weighed again; a similar and bottomless basket was fixed in the moss colony as a control.Key results and discussion:Despite promising laboratory results, the marking method gave low shoot survival in the field, probably due to the restriction of external water transport along the shoots. No differences in shoot elongation were found between the plug method and the control. The plug method comprises the measurement of both apical and lateral growth, and the authors of the present study therefore recommend it for measuring the growth of brown mosses with numerous lateral branches. Considering only the elongation of the top shoots leads to an underestimation of growth by 50% and consequently to an underestimation of the peat-forming potential of brown mosses.

Peat formation is the key process responsible for carbon sequestration in peatlands. In rich fens, peat is formed by brown mosses and belowground biomass of vascular plants. However, the impact of ecohydrological settings on the contribution of mosses and belowground biomass to peat formation remains an open question. We established seven transects in well-preserved fens in NE Poland along an ecohydrological gradient from mesotrophic sedge-moss communities with stable water levels, to more eutrophic tall sedge communities with higher water level fluctuations. In each transect, we measured the production of brown mosses (using the plug method), aboveground vascular plant biomass (one year after cutting) and belowground biomass (using ingrowth cores). Decomposition rates of all biomass fractions were assessed using litter bags. The first-year surplus of potentially peat-forming fractions, i.e., mosses and belowground biomass, decreased with increasing water level fluctuations and along a vegetation gradient from sedge-moss to tall sedge communities. Moss production was highest in the sedge-moss fen with a stable water level at the ground surface. We did not detect any difference in belowground biomass production across the gradient but found it to be consistently higher in the upper 0-5 cm than in the deeper layers. The decomposition rate also showed no response to the gradient, but differed between biomass types, with aboveground biomass of vascular plants decomposing 2.5 times faster than belowground biomass and mosses. Pattern of peat formation potential along the ecohydrological gradient in rich fen was strongly driven by brown moss production. Sedge-moss fens with a stable water level at the ground surface have the highest peat formation capacity compared to other vegetation types. In the part of the gradient that is poorer in nutrients, vascular plants invest in belowground production, and mosses dominate the aboveground layer.

Nutrient availability determines vegetation patterns and ecological functioning of intact groundwater‐fed peatlands (fens). Bryophytes, commonly referred to as ‘brown mosses', dominate calcareous fens (rich fens), are an integral part of their unique biodiversity and contribute significantly to peat formation and carbon sequestration. Brown mosses are replaced by vascular plants as nutrient availability increases. The decline of brown mosses may either be due to their physiological intolerance of high nutrient levels or to them being outcompeted by vascular plants. We aimed to distinguish between these two hypotheses by investigating whether the ecological optima reflect the physiological optima of brown mosses. Eight brown moss species, common in calcareous fens of the northern hemisphere, were grown under a gradient of nitrogen and phosphorus availability. Biomass increment, chlorophyll content and biomass nutrient concentration were measured. All brown moss species studied achieved the highest growth rates and chlorophyll contents when grown under conditions of nitrogen and phosphorus concentrations higher than those where they occur naturally at the highest frequency. Two of the species showed no growth saturation even at the highest levels of nutrient availability, while the others appeared potassium‐limited at the highest N and P levels. Brown mosses dominate natural fens at the lower edge of their physiological optimum in terms of nutrient availability, i.e. their realized niche is much narrower than the fundamental one. Based on the literature, we argue that it is the competition for light with vascular plants which limits the occurrence of brown mosses in nutrient‐rich habitats and prevents them from occupying their entire fundamental niche.

&lt;p&gt;Mires remain the most significant terrestrial carbon stock of the world. The most up to date research results have informed that former estimates of the amounts of carbon stored in mires can be underestimated by even as high as 100%. Dominant direct drivers of mire status originate from hydrology, namely the type (i.e., rain- or groundwater feeding) and quantities of water supplied to a mire and removed from this system in result of natural drainage and evapotranspiration. Impaired peat accumulation processes can result in a positive feedback of the emission of CO2 as a response to supply of mineral-rich groundwater (resulting from permafrost thaw and increase of the fen catchment area in Arctic palsa mires) and water balance changes (resulting from shortages of water in temperate fens and sloping fens). FORCE project is focused at the verification of the hypothesis that ET-driven and catchment-change driven water balance and carbon balance changes on different mires in Arctit-to-temperate transect remains in a positive feedback with the abrupt climatic changes, resulting in expected decrease of carbon accumulation in peatlands and an increased emission of greenhouse gasses that will likely not to be stopped by any management measures. In order to verify this hypothesis we formulated set of research tasks based on general context analysis, groundwater flow modelling, Monte-Carlo parameter estimation and statistical techniques of risk assessment, isotope analyses of groundwater, surface water and vegetation and emission quantification to be integrated in a Bayesian belief approach. All of the research activities were based on the results of original data collected in a number of scheduled field research campaigns . Study sites represent the most significant examples of mires exposed to abrupt climat-change-related issues across the Arctic-to-temperate gradient: from Nordic permafrost (Suossjarvi) through the bog-lake system with expected significant role of aquatic ecosystems in total CO2 and CH4 balance (Midtfjellmosen), to fens in river valley dependent both on the draining role of the river and limited supply of water to the mire (Rospuda Valley, PL). In the framework of the project (i) we plan to reveal the amounts of CO2 transported by groundwater to the mires analysed and see how does the probable emission of CO2 from groundwater in mires contribute to total emission of CO2 from mires; (ii) we will establish groundwater flow models in order to reveal the origin of water supplying particular objects and its changes in modelled abrupt climatic change scenarios represented as changed parameters of ET, P in a Monte-Carlo procedure; (iii) we will assess the isotope composition of groundwater and surface water in order to confirm the origin of water feeding particular zones of the mire and calibrate groundwater flow models; and (iv) we will conduct laboratory estimation of greenghouse gasses and groundwater quality. It is likely that the messages resulting from the FORCE project implementation will influence international strategies oriented at promotion of mire research and conservation, placing new threads of peatland hydrology, emissions and carbon accumulation in a management context.&lt;/p&gt;

The aim of this study was to understand the variation in traits relevant for desiccation avoidance among bryophyte species dominant in rich fens and to assess whether these traits explain the formation of a hummock-hollow gradient within peatlands. In samples of 10 species (Aulacomnium palustre, Calliergonella cuspidata, Climacium dendroides, Hamatocaulis vernicosus, Helodium blandowii, Marchantia polymorpha, Plagiomnium ellipticum, Sphagnum teres, S. warnstorfii, Tomentypnum nitens) collected in rich fens of NE Poland, we calculated: canopy bulk density of wet (CDW) and dry (CDD) colonies, maximum water content of bryophyte colonies (WCmax), desiccation rate (K), shoot area index (SAI), canopy dry mass per surface-projected area (CMA), and specific leaf area of a whole living bryophyte part (SLA). The hummock-forming frequency was quantified for each species in the field. Sphagna had the highest WCmax, SAI and CDW, T. nitens and C. dendroides had the lowest WCmax and SLA, P. ellipticum had the highest K, the lowest CMA and CDD. Hummock-forming frequency was positively correlated with CMA and generally negatively related to K, with exception of H. vernicosus showing a high water-retaining ability (low K) despite a hollow or lawn form of growth.

In wet peatlands, plant growth conditions are largely determined by local soil conditions, leading to locally adapted vegetation. Despite that Carex species are often the prevailing vascular plant species in fen peatlands of the temperate zone, information about how these species adapt to local environmental conditions is scarce. This holds true especially for below-ground plant traits and for adaptations to fen-typical nutrient level variations. To address this research gap, we investigated how different geographic origins (Germany, Poland, The Netherlands) of C. acutiformis and C. rostrata relate to their response to varying nutrient availability. We performed a common garden experiment with a controlled gradient of nutrient levels, and analyzed above- and below-ground biomass production of both Carex species from the different geographic origins. We related these traits to environmental conditions of the origins as characterized by vegetation composition-derived indicator values for ecological habitat conditions. While we detected high above-ground phenotypic plasticity of Carex from different origins, our data point to below-ground genotypic differences, potentially indicating local adaptation: Rhizome traits of C. rostrata differed significantly between origins with different nutrient indicator values. These results point towards differences in C. rostrata clonal spread behavior depending on local peatland conditions. Therefore, local adaptations of plant species and below-ground biomass traits should be taken into account when studying peatland vegetation ecology, as key functional traits can differ between genotypes within a single species depending on local conditions.