Nitrogen Deposition Effects on Carbon Dioxide and Methane Emissions from Temperate Peatland Soils

Abstract

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 CO 2 and CH 4 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 CO 2 and CH 4 from these soils. Nitrogen availability (extractable NH 4 + ) 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 CO 2 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 CO 2 emission was positively related to soil pH (r 2 = 0.64). Additional N supply led to pH reduction and to lower CO 2 emission, especially in the low N peat soils. Thus, increased atmospheric N deposition leads, probably as a result of soil acidification, to lower CO 2 emission. Although glucose amendments resulted in increased CO, and CH 4 emission, we did not find evidence that this was caused by increased mineralization of native peat. Mean daily CH 4 -C emission was about 1-2 orders of magnitude lower than mean daily CO 2 -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 (r 2 =0.42-0.55), whereas a multiple regression model revealed that methane emission was determined by N-related soil chemistry variables (r 2 = 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 CO 2 -C emission and CH 4 -C emission and the ratio of their global warming potentials (1:21).