Effects of liming and nitrogen fertilization on emissions of CO2 and N2O from a temperate forest

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Abstract
Fluxes of N2O and CO2 were measured simultaneously in control, N‐fertilized, and limed plots in a 145‐year‐old beech stand in the Solling area in Germany using an automated chamber method. The N‐fertilized plot received annually 140 kg of nitrogen as NH4SO4 since 1982; the limed plot was treated with 30 t/ha of dolomitic limestone once in 1982. On all plots, fluxes of N2O and CO2 underwent strong diel, daily, and seasonal variations. For the control plot, N2O and CO2 effluxes averaged about 1 mg N/m2/d and 2.9 g CO2/m2/d from October until May and 3 mg N/m2/d and 4.5 g CO2/m2/d from May until September. Annual fluxes for N2O and CO2 were 5.6 kg N/ha/yr and to 3.2 t C/ha/yr, respectively. Nitrogen saturation of the system due to high rates of N deposition for several decades may be responsible for the high N2O losses. Liming drastically reduced the N2O emission to 1.5 kg N/ha/yr and increased the CO2 emission to 4.1 t C/ha/yr, 5 years after the treatment. Changes in N2O/N2 ratios are assumed to be the reason for the lower N2O emission. Fertilization increased the N2O emission, resulting in 7.8 kg N/ha/yr, whereas the effect on CO2 emission with 3.8 t C/ha/yr was less pronounced.