Document: ANN-3-58-33

Seasonal patterns of denitrification controls in three vegetation types of southeastern Oklahoma.

WEST, A.E.* ^1,3 and E.E.JORGENSEN ^2,3

Oak Ridge Institute for Science and Education (ORISE), Ada, OK 74820 USA ¹
US Environmental Protection Agency (EPA) ²
R.S. Kerr Environmental Research Center, Ada, OK 74820 USA ³

Abstract:
Seasonal patterns in the factors limiting denitrification were determined for the soils of three natural plant communities of southeastern Oklahoma. Soil samples were taken from beneath oak, Eastern redcedar, and grasses. Using the acetylene block method, we measured denitrification on soil subsamples that were amended with either potassium nitrate, carbon substrates (glucose, fructose, sodium acetate, and glutamic acid), or both. Denitrification in unamended soils ranged from undetectable to 120 pmol per g d.w.. In oak and grass soils in spring, denitrification was stimulated by nitrate. As soils dried and warmed with the onset of summer drought, denitrification was stimulated by carbon, but not by nitrate, indicating that denitrification became carbon-limited. Anaerobic conditions did not stimulate denitrification unless carbon substrates were also added. Thus it was concluded that carbon did not stimulate denitrification solely by reducing oxygen availability. In oak and grass soils, more denitrification occurred in the top layer of soil. This suggested that leaf litter was a major carbon source for denitrifiers in these soils. To test this, the stimulation of denitrification by aqueous leaf litter extracts was measured. Stimulation of denitrification by leaf litter extracts correlated with the dissolved organic carbon content of the leaf litter extracts (p<0.01).

Keywords: denitrification, soil, leaf litter

This abstract is being presented at: 3:30 PM in session:
MICROBIAL ECOLOGY