Differences in the nitrous oxide emission and the nitrifier and denitrifier communities among varying aggregate sizes of an arable soil in China

Soil aggregates play a vital role in regulating soil biological processes such as those involved in microbial nitrogen (N) reactions. Here, a microcosm experiment was conducted to evaluate the differences in nitrous oxide (N2O) emissions and their associated microbial communities among varying soil aggregates (4-8, 2-4, and < 1 mm) separated from an arable soil. Real-time quantitative polymerase chain reaction and terminal restriction fragment length polymorphism determined the abundances and community compositions of amoA-containing bacteria (AOB) and archaea (AOA), and denitrifiers containing narG or nosZI. Significant (P < 0.05) differences in the N2O fluxes occurred among the soil aggregate sizes, with smaller aggregates emitting higher N2O fluxes, irrespective of soil moisture levels. More N2O was emitted from the soil aggregates at 35% than at the 25% gravimetric water content (theta(g)). In general, higher abundances of nitrifier and denitrifier gene copies were found in smaller aggregates, except for the denitrifiers containing nosZI at 25% theta(g) and AOA at 35% theta g. Moreover, the community compositions of AOA and denitrifiers containing narG and nosZI varied significantly among the different soil aggregate sizes. Differences in the N2O fluxes were affected by the abundance and community composition of denitrifiers containing narG, whereas the influence of other microbes on the N2O fluxes mainly depended on soil moisture conditions. Therefore, soil aggregates influenced N2O emissions by altering the abundance and community compositions of the nitrifiers and denitrifiers, and small soil aggregates were the preferred microenvironments for the growth of nitrifiers and denitrifiers.