Ammonia oxidising populations and relationships with N2O emissions in three New Zealand soils

Nitrous oxide (N2O) emissions from intensively grazed pasture systems contribute significantly to total greenhouse gases. A series of field-plot experiments were conducted at three geographically separated sites to study the ammonia oxidising microbial populations and their relationships with N2O emissions. Our results support the findings from earlier incubation experiments, showing that growth of ammonia oxidising bacteria (AOB), and not ammonia oxidising archaea (AOA), was stimulated by the high concentration of urine. There was substantial spatial variability of the AOB and AOA amoA gene copy numbers at different sites and within replicate samples. AOB abundance was generally higher in the top 2.5 cm compared with the top 10 cm of soil, whereas the opposite trend was observed for AOA. Positive relationships were found between the N2O emissions and AOB abundance, although the relationship varied at the three sites.