Full-cycle greenhouse gas balance of a Sphagnum paludiculture site on formerbog grassland in Germany

The cultivation of peat mosses on rewetted peatlands (= Sphagnum paludiculture) is a promising alternative to drainage-based land use, as the production function is maintained while greenhouse gas (GHG) emissions are reduced. However, to date, GHG exchange studies that cover the entire production system and a complete production cycle are missing. Therefore, we combined data from the establishment phase (2011-2013) with data from the production phase (2017-2018) of a seven-year Sphagnum paludiculture in northwestern Germany including export by harvest. GHG exchange was recorded on all elements of the production system (Sphagnum production fields, ditches, causeways) with closed chamber measurements. Over the entire production cycle, Sphagnum production fields represented net GHG sinks of -3.2 ± 4.2 t ha-1 a-1 (in CO2-eq), while ditches and causeways were GHG sources of 13.8 ± 11.5 and 29.3 ± 9.8 t ha-1 a-1, respectively. Corrected for the percentage of area of each element of the production system and including partial harvest of peat moss (in dry matter) of ~13.8 ± 0.6 t ha-1, Sphagnum paludiculture was a net GHG source of 10.7 ± 4.6 t ha-1 a-1, reducing net GHG emissions by ~20 t ha-1 a-1 compared to grassland on drained organic soils. Per ton of dry biomass harvested, Sphagnum paludiculture emitted 9.9 ± 4.6 t CO2-eq. Because of their high area share, causeways contributed the most to net warming, suggesting a reduction in causeway area in future Sphagnum paludiculture. Therefore, a realistic future "best practice" approach features area percentages of 80% Sphagnum production fields, 5% ditches, 15% causeways, and a full biomass harvest, with the top 5 cm of harvested peat moss lawn used on-site for reseeding Sphagnum production fields. This approach reduces CO2 equivalent emissions from Sphagnum paludiculture to up to 4.3 ± 1.9 t ha-1 a-1 or 0.9 ± 2.1 t per ton of dry matter harvested.