Differential Responses of Ammonia Oxidizers in a Pasture Land with a History of Poultry Litter Application.

Poultry litter is a valuable source of nutrients which is frequently applied to pastures. To examine the changes in soil ammonia oxidizer (AO) communities in response to long-term PL application, we collected samples from plots in GA where PL was applied twice a year @ 5 Mg per ha for several years.  Soil samples were collected in 2009 (after 15 years of PL application) and 2013 (after 2 years of stopping PL application) at the depths of 0-5 and 0-15 cm. The control plots received Urea Ammonium Nitrate (UAN) at an equivalent rate of N content in PL. Quantitative PCR, Denaturing Gradient Gel Electrophoresis, amoAC intergenic spacer analysis (AISA) methods were used to study the abundance and community structure of soil AO. PL treated plots had higher copy numbers of AO than the control plots, with ammonia oxidizing archaea (AOA) being outnumbered by ammonia oxidizing bacteria (AOB). As the PL application was discontinued, a significant decrease in copy numbers for AOB was observed. The majority of the bacteria belonged to Nitrosospira spp. The changes in the community composition of AOB represented as Shannon index of Diversity were significant between 2009 and 2013 in the 0-15 cm depth. We will also report results from an incubation study to quantify the relative contributions of AOA and AOB to total nitrification and corresponding relationships with total bacterial and denitrifier populations.