Processes contributing to nitrite accumulation and concomitant N2O emissions in frozen soils

The objectives of this study were to determine the processes leading to NO2− accumulation and its contribution to N2O emissions in frozen soils. Soil microcosms were incubated for 21 days under frozen (−2 °C) or unfrozen (+0.5 °C) conditions. Soils were amended with either 15N-NH4+ or 15N-NO3 to quantify the contribution of nitrification and denitrification processes to NO2− accumulation, respectively. Production of 15N-N2O was measured to determine the contribution of NO2− accumulation to N2O emissions. Nitrite progressively accumulated over 21 days in soils incubated at −2 °C to concentrations up to 8.87 μg N g−1 dry soil. However, in soils incubated at +0.5 °C, NO2− concentration increased from day 0 to day 7 (up to 3.61 μg N g−1 dry soil) and declined thereafter. At both temperatures, NO2− accumulation was associated with a progressive decrease in NO3− concentration while NH4+ concentration remained relatively stable over time. Greater N2O emissions were observed at +0.5 °C (average of 0.0135 μg N g−1 dry soil h−1) compared with −2 °C (average of 0.0045 μg N g−1 dry soil h−1) from day 2 to day 14. However, N2O emissions were 3.5 fold greater at −2 °C compared with +0.5 °C on day 21. In soils at −2 °C, 97.40–99.75% of the NO2− and over 99.56% of N2O were derived from NO3−. In soils incubated at +0.5 °C, the proportions of NO2− and N2O derived from NO3− slightly decreased while the pr...

Source: Soil Biology and Biochemistry - August 15, 2018 Category: Biology Source Type: research