Wednesday, November 15, 2006 - 9:00 AM

Connecting Community Structure, Kinetics and Process: Nitrification in Dairy Waste Treated Soils.

Jeanette M. Norton1, Mussie Y. Habteselassie2, Teresa E. Koper1, John Stark3, and Bruce E. Miller4. (1) Utah State Univ, Dept of Plants, Soils and Biometeorology, Logan, UT 84322-4820, (2) Purdue Univ, Dept of Agronomy, 915 W. State Street, West Lafayette, IN 47907, (3) Dept of Biology, Utah State Univ, 5305 Old Main Hill, Logan, UT 84322-5305, (4) Ag Systems Tech.& Educ, Utah State Univ, 2300 Old Main Hill, Logan, UT 84322

The objective of this study was to gain insight into the functional diversity of ammonia-oxidizing bacteria (AOB) in agricultural soils treated with dairy-wastes. We wanted to make connections between the diversity of these nitrifying bacteria and the kinetics of the nitrification process. The kinetic characteristics were determined for agricultural soils treated with (NH4)2SO4, dairy compost or no N amendment repeatedly over a five year period. The relationship between NH4+ substrate concentrations (ranging from 0 mM-20 mM NH4+) and nitrification rate was examined in soil-slurry laboratory experiments. The rate data were fit to both the Michaelis-Menten and Haldane kinetic models. All the soils exhibited decreased rates or NH4+inhibition at concentrations higher than 2 mM NH4+. Therefore, the Haldane model fit the data better than the standard Michaelis Menten model. Vmax was higher in the N treated soils versus the no N control and was the only parameter that was significantly different between soil treated differentially. While kinetic parameters such as Km may reflect differences in AOB community composition; in this study we did not find significant differences in Km. Therefore, we would not expect to find significant AOB community differences between these soils. This was confirmed by extraction of DNA from the soils and analyses of clone libraries of partial amoA genes. All soil AOB communities were found to be dominated by strains related to Nitrosospira multiformis. The kinetics of soil AOB cultures enriched under low NH4+ concentrations from these same soils are under further examination.