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

Abstract

Emissions of NO, NO2, and N2O 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 N2O (up to 86%) emissions for individual soils, but average emissions differed significantly between various forest soils. Generally, NO and N2O 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 N2O emissions from this soil tended also to be highest (171.7 ± 42.2 μg N2O‐N m−2 h−1), but did not differ significantly from other soils. NO2 deposition occurred in all soils and strongly correlated to NO emissions. NO and N2O emissions showed a positive exponential relationship to soil temperature. With activation energies between 57 and 133 kJ mol−1, N2O 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. N2O emissions increased with increasing water filled pore space (WFPS) or decreasing water tension, respectively. Maximal N2O 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.