Using Transcripts Abundance to Identify the Origin of Nitrous Oxide Emissions During Soil Wet-Up

The first rainfall following the dry, hot summer in arid and semi-arid ecosystems results in large fluxes of trace gases, including nitrous oxide. Although nitrous oxide can be produced as the result of denitrification or nitrification in soils, it is generally assumed that large fluxes of nitrous oxide originate from denitrification. We measured nitrous oxide production over three days following water addition to a California grassland soil, and we found emissions of nitrous oxide as high as 21 ng N2O-N /g /d, rivaling those of wetland ecosystems. We also measured transcript abundances for nitrite reductase (nirK) and nitrous oxide reductase (nosZ) over the same period in order to relate denitrifier transcriptional response to nitrous oxide flux. We used transcripts for ammonia monooxygenase (Bacterial and Archaeal amoA) to try to identify nitrous oxide emissions that could be the result of nitrification. Our results suggest that the primary source of these large nitrous oxide pulses may be nitrification, with both amoA transcripts and nitrous oxide emissions peaking about 9 hours after water addition.