Methane and nitrous oxide fluxes, and carbon dioxide production in boreal forest soil fertilized with wood ash and nitrogen

Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N2O emission and suppress CH4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO2 emission. The fluxes of CH4, N2O and CO2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH4 oxidation potential, CO2 production, net nitrification and N2O production were studied in laboratory incubations. The mean in situ N2O emissions and in situ CO2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 mu g N2O m(-2) h(-1) and from 533 to 611 mg CO2 m(-2) h(-1). However, ash increased the CH4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH4 uptake rates in situ. The mean in situ CH4 uptake rate in the untreated, N, ash and ash + N plots were 153 +/- 5, 123 +/- 8, 188 +/- 10 and 178 +/- 18 mu g m(-2) h(-1), respectively.