Effects of soil moisture and temperature on NO, NO2, and N2O emissions from European forest soils

Abstract

Emissions of NO, NO 2, and N 2 O to the atmosphere were measured with a fully automated laboratory system from undisturbed soil columns obtained from five different temperate and one boreal forest sites. The soils were chosen to cover a transect through Europe, sandy and loamy textures, and different atmospheric nitrogen deposition rates. In a two‐factorial experimental design, soil cores were kept under varying conditions with respect to temperature (range 5–20°C) and soil moisture (range 0–300 kPa). The combination of soil temperature and soil moisture could explain a better part of variations in NO (up to 74%) and N 2 O (up to 86%) emissions for individual soils, but average emissions differed significantly between various forest soils. Generally, NO and N 2 O were emitted from all soils except from the boreal pine forest soil, where NO was consumed. NO emissions from the German spruce forest receiving highest yearly nitrogen inputs of >35 kg ha−1 yr−1 ranged from 1.3 to 608.9 μg NO‐N m−2 h−1 and largely exceeded emissions from other soils. Average N 2 O emissions from this soil tended also to be highest (171.7 ± 42.2 μg N 2 O‐N m−2 h−1), but did not differ significantly from other soils. NO 2 deposition occurred in all soils and strongly correlated to NO emissions. NO and N 2 O emissions showed a positive exponential relationship to soil temperature. With activation energies between 57 and 133 kJ mol−1, N 2 O emissions from the various soils responded more uniformely to temperature than NO emissions with 41 and 199 kJ mol−1. The two Austrian beech forest soils showed exceptionally high activation energies for NO emissions, which might be attributed to chemodenitrification. N 2 O emissions increased with increasing water filled pore space (WFPS) or decreasing water tension, respectively. Maximal N 2 O emissions were measured between 80 and 95% WFPS or 0 kPa water tension. Optimal moisture for NO emission differed significantly between the soils, and ranged between 15% WFPS in sandy Italian floodplain soil and 65% in loamy Austrian beech forest soils. These differences may be related to the specific adaptation of the microbial communities to draught conditions.