Globally, peatlands are estimated to store about 600 Pg of carbon (C), or about 30% of global soil C stocks, although estimates vary widely (Minasny et al. 2019, 2023; Leifeld and Menichetti 2018). This makes peatland C stocks about twice as high as the C in the above- and belowground biomass of living forests (Pan et al. 2013). Since the industrial revolution, northern peatlands in the temperate and boreal zones of the Northern Hemisphere have been extensively drained for agricultural production, a trend that only stopped about half a century ago, with peatland areas used as cropland declining since the 1990s due to abandonment (Qiu et al. 2021). In contrast, large-scale drainage and conversion of tropical peatlands began half a century ago, driven by increasing land use pressures, first in Southeast Asia, but increasingly also in Africa and South America (Fluet- Chouinard et al. 2023, Leifeld et al. 2019; Miettinen et al. 2017; Frolking et al. 2011). Drainage of peat soils accelerates microbial carbon and nitrogen mineralization due to the change from anoxic to oxic conditions (Ma et al. 2022; Frolking et al. 2011), so that with drainage peatlands become strong sources of the greenhouse gases (GHG) CO2 and N2O, while CH4 emissions mostly disappear (Frolking et al. 2011). The importance of drained peatlands as regional and global GHG sources is huge, especially in Northern Europe, North America and South-East Asia, although the accounting is somewhat hampered due to uncertainties in peatland mapping and definitions, and the extent and intensity of anthropogenic activities affect the GHG balance of peatlands (Minasny et al. 2023; Harris et al. 2022). For example, GHG emissions associated with peatland drainage are estimated to contribute about 50% of total GHG emissions from land use, land use change, and forestry (LULUCF) sector in Indonesia (Austin et al. 2018) and still 6.6% of total anthropogenic GHG emissions in a highly industrialized country such as Germany (Tiemeyer et al. 2020).

Peatland restoration has become a key measure to reduce GHG emissions from the LULUCF sector, which is due to the importance of drained peatlands as GHG sources and of intact peatlands as sinks for atmospheric CO2 resulting from the hindered decomposition of plant litter inputs under anaerobic conditions (Frolking et al. 2011),. The European Union, as well as many of its Member States, Canada, the USA, but also countries in the tropics such as Indonesia, are currently assessing strategies and support schemes for the rewetting of drained peatlands used for agriculture or forestry, although a regulatory framework is not yet in place (Chen et al. 2023; Wicaksono and Zainal 2022). Such strategies include the use of rewetted peatlands for sustainable biomass production, such as for paludiculture (Freeman et al. 2022).

In November 2022, the Department of Agroecology and its Pioneer Center on Sustainable Agricultural Futures, Land-CRAFT, Aarhus University, Denmark, organized a workshop to bring together leading experts in peatland ecology and management to discuss what can be done to mitigate greenhouse gas (GHG) emissions and restore carbon stocks in drained organic soils (Fig. 1). The workshop discussed the latest research on regulating GHG emissions from managed peatlands and organic soils, as well as possible ways to restore the original functions of peatlands as important landscape elements for carbon storage, water and nutrient buffering, and biodiversity. Policy developments at both national and international levels were addressed, as well as ways to incentivize peatland restoration. This last point remains critical because, given the large uncertainties associated with quantifying the extent of managed peatlands and their GHG balance, and the lack of knowledge on the longer-term mitigation effects of rewetting, the inclusion of GHG emission reductions from rewetting in national GHG inventories reported to the UNFCCC remains problematic and hampers the targeting and identification of appropriate mitigation actions and thus policy making (Fig. 2).

Fig. 1
figure 1

The intensity of greenhouse gas emissions within peatlands and their consequent impact on global warming potential are intricately shaped by soil quality, nutrient levels, pH, biodiversity comprising both plant and microbial communities, and notably, the water table’s fluctuations in the area. The direction of blue arrows denotes how fluxes of nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) are stimulated. It’s noteworthy that the microbial turnover of carbon (C) in soils is inherently intertwined with the nitrogen (N), phosphorus (P), iron (Fe), and sulfur (S) cycling (Zak et al. 2022)

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The special issue on “Peatlands for climate change mitigation in agriculture” provides a comprehensive overview of different aspects of peatland research, covering aspects of organic matter decomposition, management of peatlands used for agriculture, peatland degradation in the tropics, assessment of rewetting strategies and, finally, observational shortcomings regarding peatland mapping.

Two papers in this collection assess the dynamics of organic matter mineralization in different peatland types. The work by Glatzel et al. (2023) assesses mineralization dynamics and dissolved organic matter fluxes in two common peatland types, blanket bogs and raised bogs. They found that blanket bogs have higher hydrological C losses compared to raised bogs due to greater hydrological conductivity to the adjacent landscape. Insights into the decomposition of organic matter and possible pathways of CH4 production are provided by an in-situ decomposition study in a rewetted peatland with Phragmites litter by Reuter et al. (2023). This study shows that the highest rates of carbohydrate decomposition were observed in the still aerobic surface water layers of the rewetted peat, while in the deeper, mostly anaerobic but still rooted peat layers, lignin was decomposed more efficiently. The authors speculate that the significant CH4 production may be directly related to the demethoxylation of phenols. For assessing emission risks associated with rewetting it would be helpful to identify by chemical makers the degree of peat degradation. Turunen et al. (2024) used a C:N:H stochiometric approach for classifying the status of peat degradation and changes in peat substrate quality following water table changes. They showed that elemental ratios of H:C, O:C and C:N and degree of unsaturation are valuable proxies for peat degradation and for explaining site differences in annual CO2 and CH4 emissions.

The study by Honkanen et al. (2023) confirms that drained peatlands used for agriculture in Finland are major sources of GHG, with C loss rates of about 5.4–8.8 t C ha−1 yr−1, N2O emissions in the range of 4.5–11.8 kg N ha−1 yr−1. CH4 fluxes were marginal, with soils acting as weak sinks. The introduction of no-tillage reduced GHG emissions by about 10%, although this remains uncertain as inter-annual variability was significant and longer-term monitoring beyond the three-year observation period is needed to confirm observations. A somewhat different view of GHG emissions from agricultural peatlands is provided by the study of Tyler and Silver (2023), who compared three different management systems in the Sacramento-San Joaquin Delta of California. While the perennial alfalfa and grazed pasture sites were overall net sinks for GHGs, the peatland used for corn production was a strong sink for both CO2 (about 60% of total GHG emissions) and N2O (about 40%). Most interestingly, hotspots of CO2, CH4 and N2O did not persist over the observation period, and the explanatory power of spatiotemporal variations in soil moisture, soil oxygen and temperature for explaining patterns of GHG fluxes remained limited.

The effect of different restoration pathways on the GHG budgets of peatlands is the focus of four papers in this special issue. Temmink et al. (2023) investigated nutrient dynamics, organic matter formation, and carbon and nutrient accumulation in a 16 ha Sphagnum paludiculture site in NW Germany 10 years after topsoil removal and Sphagnum inoculation. They conclude that Sphagnum paludiculture sequestered an average of 2.6 t C ha−1 yr−1 and thus represents a promising management strategy for peatland restoration on agricultural peatlands. The practice of topsoil removal as part of peatland restoration and for priming paludiculture remains a matter of ongoing discussion (Zak an McInnes, 2022). Käärmelahti et al. (2023) show that the establishment of Sphagnum paludiculture was comparable at topsoil removal depths of 5 or 30 cm, but that P concentrations remained elevated when no or only 5 cm of topsoil was removed. While the establishment of paludiculture appears to be an effective strategy for converting former agricultural peatlands from strong GHG sources to GHG sinks, the long-term benefits under the constraints of climate change remain uncertain. Bockermann et al. (2024) used an in-situ experimental approach with warming (+ 0.8–1.3 °C increase in mean annual temperature) and rewetting of soils to a water table position of 0.13 m below the soil surface to study the effects of climate change on intensively and extensively managed grasslands. They found that at the elevated water table position, high rates of net C sequestration could be observed even under warming conditions, and that even with huge N2O emissions of up to 27 kg N2O ha−1 yr−1, the study site turned from a strong GHG source (+ 48–67 t CO2−eq ha−1 yr−1) to a net GHG sink (− 11 to − 13 t CO2−eq ha−1 yr−1).

Fig. 2
figure 2

Peatland restoration through rewetting has been observed to trigger a swift recovery of the carbon dioxide (CO2) sink function and significantly reducing emissions of nitrogen dioxide (NO2). However, it may also lead to substantial emissions of methane (CH4), potentially exerting a positive impact on the overall global warming potential (GWP) over several decades. The restoration success hinges greatly on regional water availability, the trajectory of climatic changes, and land use practices within the catchment area. Future monitoring of peatland succession stands to benefit significantly from the utilization of advanced earth observation methods

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By reviewing the current literature and developing a conceptual model, the paper by Mander et al. (2023) provides insights into the GHG emissions and C sequestration potential of different restoration options, such as paludiculture, shallow lakes, or restored peatlands in boreal, temperate, and tropical climates. Based on their assessment, Sphagnum paludiculture showed the highest C sequestration potential, followed by shallow lakes and reed/grass paludiculture. However, the study also confirms that long-term GHG balance datasets and analyses are too scarce, and that lateral losses of dissolved and particulate organic matter and associated GHG fluxes from streams are often overlooked, to derive a comprehensive picture of drainage- and restoration-induced changes in peatland GHG fluxes (Fig. 1). An additional review synthesizes the research highlighting the pivotal role of soil microbial communities in regulating carbon and nutrient cycling within rewetted peatlands (Gios et al. 2023). This encompasses an examination of molecular biology techniques designed to better understand the biogeochemical processes linked to GHG fluxes. Notably, it demonstrates how rapidly evolving molecular biology approaches, like high-throughput sequencing, serve as potent tools in unraveling the dynamics of crucial biogeochemical processes when combined with isotope tracing and GHG measurement techniques.

The lack of observations on the effects of drainage on peatlands is particularly relevant for tropical peatlands and swamps. In a study in Sumatra, Indonesia, Swails et al. (2023) analyzed how CH4 and N2O emissions changed as a result of a land-use transition from primary peat swamp forests to oil palm plantations. This transition was associated with a large increase in soil N2O emissions, while CH4 emissions decreased significantly. Although the decrease in CH4 emissions compensated for the increase in N2O emissions using a 20-year global warming potential (GWP) approach, this was not the case when changes in GHG emissions were calculated over a 100-year period.

In addition to active drainage of tropical swamp forests and subsequent land use change, peatland degradation due to unsustainable harvesting of e.g., Mauritia flexuosa palms for fruit, affects site hydrology and GHG fluxes. A site study for a peat swamp forest in Peru (Hergoualc’h et al. 2023) and a review of published field measurements by Swails et al. (2024) for sites in Southeast Asia, Latin America and the Caribbean provide initial insights into the magnitude of GHG flux changes due to degradation. Swails et al. (2024) conclude that “the large observed increases in net CO2 emissions in undrained degraded forests compared to undegraded conditions calls for their inclusion as a new class in the IPCC guidelines” and that either protection or a new approach to sustainable management of swamp peatlands is needed to limit the impact of tropical peatland degradation on GHG emissions and the climate.

Given the importance of peatlands to the Earth’s climate system, and the extent to which human activities have changed these systems from net sinks to net sources of GHGs, it remains remarkable that key observational evidence remains inadequate. The paper by Zhao et al. (2023) provides an important analysis of current observational gaps and specifically calls for additional GHG observations in Africa, Latin America and the Caribbean, as overall assessments of the GHG balance of natural and managed peatland systems are scarce. However, targeting future measurements and restoration activities requires detailed mapping of peatlands, peatland types and conditions, and anthropogenic management activities around the world, which remains a challenge. The review by Minasny et al. (2023) summarizes various approaches to monitoring peatland conditions and functions, including remote sensing techniques with passive and active sensors that can be used at regional to national scales to support monitoring of subsidence rates, water levels, peat moisture, and GHG emissions. Improved monitoring of peatlands using comparable approaches is a prerequisite for national and international prioritization of peatland protection and restoration measures. Protecting natural peatlands and restoring those peatlands currently used for agriculture is a key priority for reducing the GHG footprint of global agriculture.

While this appears to be a win-win situation in terms of reducing national GHG emissions from the LULUCF sector, as well as being beneficial for landscape hydrology and biodiversity, the reality is still different, especially for peatlands in the tropics, where increasing agricultural land use is still a major driver of peatland drainage and conversion to agricultural land. Moreover, little is known so far about how climate change may directly or indirectly affect peatland restoration and the GHG balance, e.g., available water resources at the regional scale may not be sufficient to ensure sustained high-water table positions of rewetted peatlands across seasons and years, which may jeopardize the restoration goal of turning drained peatlands into permanent GHG sinks. Thus, the question of what role global peatlands may play in regional and global climate and hydrological systems in the coming decades remains unanswered.