Investigating the diurnal variability of nitrous oxide emissions from soils

Diurnal variations in soil nitrous oxide (N_­2O) emissions have been documented for nearly four decades yet consensus on their significance is still lacking. Resolving this question is important as soil N₂O emissions have some of the highest uncertainties in national greenhouse gas inventories. A major challenge for understanding diurnal variation is that conventional measurements rarely operate at temporal frequencies that can observe and report this phenomenon. Some higher frequency studies have observed daytime peaking of soil N_­2O emissions and often ascribe it to the diurnal oscillation of soil temperature. However, night-time peaking and irregular diurnal N_­2O patterns have also been reported in a number of studies.

To investigate the prevalence and characteristics of diurnal N_­2O variability, we systematically reviewed published studies that measured N₂O at high temporal frequencies (≥ 5 times/day). We identified 46 published studies covering cropland, grassland and forest soils; and extracted sub-daily N_­2O flux data and other soil parameters, yielding 286 individual days of data. Diurnal variability of N_­2O emissions were found in ~80% of the data, with ~60% peaking during the day and ~20% at night. Diurnal N_­2O patterns were associated with non-diurnal factors including soil texture and land use but the relationship between soil temperature and N_­2O flux was inconsistent, with strong positive correlations (R > 0.7) only found in one-third of the datasets.

This talk explores the implications of the review results on the time of sampling using conventional approaches (single time-point flux measurements), and the potential drivers of diurnal N_­2O variations for future research. In addition, this talk will also introduce a novel automated measurement technique allowing flux measurements at high temporal resolutions and how its application could enable experimental investigations of potential drivers of diurnal N_­2O variability.