Nitrogen deposition effects on carbon dioxide and methane emissions from temperate peatland soils

Northern peatlands are important sources of carbon dioxide and methane emissions to the atmosphere. Increased atmospheric N deposition may have a significant impact on the emission of these greenhouse gases. We studied CO2 and CH4 emissions from untreated temperate peat soils from a eutrophic and a mesotrophic fen in a high N deposition area (the Netherlands) and from a mesotrophic fen in a low N deposition area (north-east Poland). In addition, we investigated the effects of N, P and glucose amendments on the emissions of CO2 and CH4 from these soils. Nitrogen availability (extractable NH4+ in untreated peat from the high N area was 2.5-7.5 times higher than in the low N area, whereas the pH was 0.9-1.7 units lower. Using 6-week laboratory incubations of peat columns, we found that mean daily CO2 emission from untreated peat soils from the high N area was lower than that from the low N area. Both linear and multiple regression analysis showed that CO2 emission was positively related to soil pH (r2=0.64). Additional N supply led to pH reduction and to lower CO2 emission, especially in the low N peat soils. Thus, increased atmospheric N deposition leads, probably as a result of soil acidification, to lower CO2 emission. Although glucose amendments resulted in increased CO2 and CH4 emission, we did not find evidence that this was caused by increased mineralization of native peat. Mean daily CH4- C emission was about 1-2 orders of magnitude lower than mean daily CO2- C emission. In the untreated peat soils from the high N eutrophic site, methane emission was higher than in the high N mesotrophic site and in the low N mesotrophic site. Linear regression analysis showed a positive relation between methane emission and soil fertility variables (r2=0.42-0.55), whereas a multiple regression model revealed that methane emission was determined by N-related soil chemistry variables (r2=0.93). Increased nutrient supply initially resulted in higher methane emission from soils of both mesotrophic sites, but there was no effect on the high N eutrophic soil. These results show that increased atmospheric N deposition leads to increased methane emission from low-fertility peat soils. However, the ultimate effect of atmospheric N deposition on trace gas emissions and thereby on global warming is determined by the balance between the ratios of the change in CO2- C emission and CH4- C emission and the ratio of their global warming potentials (1:21).