Biomass yield and greenhouse gas emissions of reed canary grass in a rewetting fen peatland

Reed canary grass (RCG) grown on non-drained peatland might be a climate friendly alternative to traditional agriculture on drained peatland. This study assessed the impact of different harvest and fertilization treatments of RCG (Phalaris arundinacea, cv. Lipaula; RCG) on greenhouse gas (GHG) exchange dynamics and global warming potential (GWP) in two measurement periods (5 May 2020 to 4 May 2021, and 18 May 2021 to 17 May 2022) at a fen with shallow water tables depths (annual mean WTD of -10 cm and -8 cm, respectively). RCG was established in 2018 and in the following years, fertilised management strategies with 2 or 5 cuts per year were compared with a non-harvested scenario (0-cut). <br/><br/>Yields of RCG decreased over the years with 15.6, 11.5 and 8.9 t DM ha-1 yr-1 for the 2-cut system and 14.5, 9.4 and 8.6 for the 5-cut system in 2019, 2020 and 2021, respectively. Mean annual WTD of -13 cm in 2019 was slightly lower than the following years. In general, photosynthetic CO2 uptake was higher in treatments with active biomass management, but no significant effect of treatments on net ecosystem carbon balance (NECB) was seen because carbon export in the harvested biomass offset the increased CO2 uptake. The mean NECB of 22.5 t CO2 ha-1 yr-1 in 2021-22 across treatments was significantly lower than the mean of 38.7 t CO2 ha-1 yr-1 in 2020-21. This might be explained by the slightly increasing WTD and more precipitation in the last year, but also by a delayed effect of increasing WTD on decreased peat oxidation. Emissions of CH4 remained low (1.1–1.9 t CO2e ha-1 yr-1) while N2O emissions were relatively high (4.0-5.7 t CO2e ha-1 yr-1) without any treatment effects. The variation found within treatments across the experimental field indicated that vegetation management reduced GHG emissions in the more productive area, while leaving the vegetation unmanaged in the less productive area of the field was beneficial. <br/><br/>