Response of Nitrous Oxide and Corresponding Bacteria to Managements in an Agricultural Soil

We investigated the linkages between composition and abundance of ammonia -oxidizing bacteria (AOB) and denitrifiers and emissions of N(2)O in a summer maize (Zea mays L.) field in a calcareous, intensively managed, agricultural soil. The treatments were zero-N (control), NH(4)(+)-based fertilizer N (favoring nitrification), NO(3)(-)-based fertilizer N + glucose + soil compaction (NO(3)(-)+Glu+Com, favoring denitrification), and urea + straw (U+S, representing conventional farming practices). We observed a substantial period (approximately 1 wk) of high N(2)O emissions that commenced after N fertilization and irrigation. The highest emissions occurred in the NO(3)(-)+Glu+Com treatment. A significant positive relationship was observed between soil NH(4)(+)-N concentrations and N(2)O emissions in the NH(4)(+) and U+S treatments. In general, a positive relationship between N(2)O emissions and soil water-filled pore space (WFPS) existed when WFPS reached >55%. Community structure of AOB in the NH(4)(+) treatment during the high N(2)O emission stage, based on terminal restriction fragment length polymorphism, was similar to that in the control treatment. There were no changes in the denitrifier community structure under NO(3)(-)+Glu+Com when 53 times higher N(2)O emissions occurred than in the control. High abundance of amoA gene copies for AOB and nir gene copies for denitrifiers were detected, however, during the high N(2)O emission period in the NH(4)(+) and NO(3)(-)+Glu+Com treatments, respectively. The results indicate that N(2)O emissions were related to the abundance of AOB or denitrifiers. It remains unclear, however, whether their community composition can also have an effect on N(2)O emissions.