Controls of soil functions and greenhouse gas emissions in rewetted peatlands

Extensive peatland rewetting efforts have recently been proposed to restore these key terrestrial carbon storage systems in order to mitigate greenhouse gas (GHG) emissions. However, little is known about the effects of rewetting on peat microbial functions that are linked to GHG fluxes. A better understanding of which biotic and abiotic factors control these processes in rewetted peatlands is crucial to help guide restoration decisions with maximum climate benefits. Here, we present results exploring the effects of peat nutrient status (nutrient-rich vs. nutrient-poor) and N loading on microbial processes and GHG (carbon dioxide, methane, and nitrous oxide) production and consumption patterns in two rewetted fens. We used an automated incubation system coupled with a gas chromatograph to monitor microbial functions and GHG dynamics in rewetted peat samples under different treatments. Samples were collected at the start of a running year-long mesocosm experiment, where peat is incubated with controlled N concentrations and vegetation composition.The start point incubation data show that N loading, but not the inherent peat nutrient status, promoted N related processes such as nitrification and denitrification. Both methane production and consumption were higher in nutrient-rich peat, and were inhibited by the presence of nitrate and ammonium respectively. Methane production kinetics displayed variable patterns between nutrient-rich and -poor peat (higher initial production rate in nutrient-rich peat), yet the total amount of methane produced was similar between fens. Results also suggest that the availability of other electron acceptors than oxygen tended to increase anoxic carbon dioxide production rates in rewetted peatlands. Overall, these findings indicate that differences in chemical composition between the two similar peatland types (fens) can lead to variable GHG dynamics after rewetting, and that controls of soil functions are site-specific.We aim to use results from the endpoint of the mesocosm experiment (after 1 year of incubation) to investigate the impact of vegetation composition on soil functions, and whether N loading leads to acclimatization of GHG-related microbial functions in rewetted fens using transcriptomics combined with targeted incubations.