Synthesizing greenhouse gas fluxes across nine European peatlands and shrublands – responses to climatic and environmental changes
In this study, we compare annual fluxes of methane (CH
4), nitrous oxide (N
2O) and soil respiratory carbon dioxide (CO
2) measured at nine European peatlands (
n = 4) and shrublands (
n = 5). The sites range from northern Sweden to Spain, covering a span in mean annual air temperature from 0 to 16 °C, and in annual precipitation from 300 to 1300 mm yr
−1. The effects of climate change, including temperature increase and prolonged drought, were tested at five shrubland sites. At one peatland site, the long-term (> 30 yr) effect of drainage was assessed, while increased nitrogen deposition was investigated at three peatland sites.
The shrublands were generally sinks for atmospheric CH 4, whereas the peatlands were CH 4 sources, with fluxes ranging from −519 to +6890 mg CH 4-C m −2 yr −1 across the studied ecosystems. At the peatland sites, annual CH 4 emission increased with mean annual air temperature, while a negative relationship was found between net CH 4 uptake and the soil carbon stock at the shrubland sites. Annual N 2O fluxes were generally small ranging from −14 to 42 mg N 2O-N m −2 yr −1. Highest N 2O emission occurred at the sites that had highest nitrate (NO 3−) concentration in the soil water. Furthermore, experimentally increased NO 3− deposition led to increased N 2O efflux, whereas prolonged drought and long-term drainage reduced the N 2O efflux. Soil CO 2 emissions in control plots ranged from 310 to 732 g CO 2-C m −2 yr −1. Drought and long-term drainage generally reduced the soil CO 2 efflux, except at a hydric shrubland where drought tended to increase soil respiration.
In terms of fractional importance of each greenhouse gas to the total numerical global warming response, the change in CO 2 efflux dominated the response in all treatments (ranging 71–96%), except for NO 3− addition where 89% was due to change in CH 4 emissions. Thus, in European peatlands and shrublands the effect on global warming induced by the investigated anthropogenic disturbances will be dominated by variations in soil CO 2 fluxes.