Microbial utilization of low molecular weight organic carbon substrates in cultivated peats in response to warming and soil degradation. Soil Biology and Biochemistry,

Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yr−1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Reducing drainage depths is, therefore, essential for responsible peatland management. Peatland restoration can substantially reduce emissions. However, this may conflict with societal needs to maintain productive use, to protect food security and livelihoods. Wetland agriculture strategies will, therefore, be required to adapt agriculture to the wetland character of peatlands, and balance GHG mitigation against productivity, where halting emissions is not immediately possible. Paludiculture may substantially reduce GHG emissions but will not always be viable in the current economic landscape. Reduced drainage intensity systems may deliver partial reductions in the rate of emissions, with smaller modifications to existing systems. These compromise systems may face fewer hurdles to adoption and minimize environmental harm until societal conditions favour strategies that can halt emissions. Wetland agriculture will face agronomic, socio‐economic and water management challenges, and careful implementation will be required. Diversity of values and priorities among stakeholders creates the potential for conflict. Successful implementation will require participatory research approaches and co‐creation of workable solutions. Policymakers, private sector funders and researchers have key roles to play but adoption risks would fall predominantly on land managers. Development of a robust wetland agriculture paradigm is essential to deliver resilient production systems and wider environmental benefits. The challenge of responsible use presents an opportunity to rethink peatland management and create thriving, innovative and green wetland landscapes for everyone's future benefit, while making a vital contribution to global climate change mitigation.

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Drainage and cultivation of peat soils almost always result in rapid soil degradation and a loss of soil organic matter (SOM). Winter cover crop cultivation and subsequent incorporation and watertable elevation have been considered as potential strategies to improve soil quality and decrease nutrient loss in drained and cultivated peatlands. However, the combined effect of residue incorporation and watertable management on greenhouse gas (GHG) emissions in these highly productive fen peat soils remains unknown. In the present study, two winter cover crops with contrasting carbon/nitrogen ratios (vetch [Vicia sativa], 45–60; rye [Secale cereale], 13–14) were incorporated into peat soils as green manure (without extra synthetic/organic N addition) at two watertable depths (−50 and −30 cm). Our results showed that fast mineralization of incorporated residues can cause a large pulse of GHG release under favourable environmental conditions. Both vetch and rye incorporation increased CO2 emissions compared with the bare soil treatments due to labile C addition and removal of N constraints. However, the two cover crops had strongly contrasting effects on N2O emissions. Incorporation of low C/N ratio vetch stimulated N2O emissions (average 21.8 ± 7.3 mg N m−2 hr−1) compared with the bare soil treatments, whereas high C/N ratio rye decreased N2O emissions (average 0.09 ± 0.03 mg N m−2 hr−1). Raising the watertable slightly reduced CO2 emissions from an average of 1.3 ± 0.4 (the bare soils) to 0.9 ± 0.3 g C m−2 hr−1 by inhibiting SOM mineralization but significantly increased N2O emissions in the vetch treatments by stimulating denitrification. CH4 fluxes were not affected by watertable depth, and their contribution to total global warming potential was negligible. Therefore, we conclude that high C/N ratio cover crops (e.g., rye) in combination with a raised watertable may represent a viable management option to mitigate GHG fluxes in fen peat soils.