2008 Joint Annual Meeting (5-9 Oct. 2008): Quantity and Diversity of Denitrifying Genes in Different Land-Use Impacted Soils of the Lower Mississippi River Valley.
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745-11 Quantity and Diversity of Denitrifying Genes in Different Land-Use Impacted Soils of the Lower Mississippi River Valley.



Wednesday, 8 October 2008
George R. Brown Convention Center, Exhibit Hall E
Hee-Sung Bae, Dept of Environmental Studies, Louisiana State University, 3161 Energy Coast and Environment Bldg, Baton Rouge, LA 70803, Stephen P. Faulkner, USGS National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, LA 70806, Josh Mire, Louisiana State University, Depatment of Environmental Studies, Baton Rouge, LA 70803 and Aixin Hou, Louisiana State University - Agronomy & Environmental Management, Louisiana State University, Dept. of Environmental Studies, Baton Rouge, LA 70803
During the last 200 years over 75% of the original riparian forests of the Lower Mississippi Valley has been converted to other land uses, mainly agriculture. This conversion has radically changed the biogeochemical functionality of the altered ecosystems, in particular their ability to retain and process N.  This study focused on assessment of land use impact on denitrifying bacterial populations that play an important role in removing nitrogen from the Lower Mississippi River Valley.  The population size of denitrifying bacteria was quantified via real-time PCR technique targeting denitrifying genes, namely nitrate reductase gene (narG), nitrite reductase gene (nirK and nirS), and nitrous oxide reductase gene (nosZ) in soils from forested wetland (FR), cultivated agricultural land (AG), and restored conservation reserve site (SBR).  The copy number of narG, nir (nirK+nirS), and nosZ per gram soil ranged from 1.1 x 106 to 1.2 x 107, 8.8 x 106 to 4.0 x 107, and 8.7 x 106 to 3.5 x 107, respectively. The highest copy number of narG and nir genes was observed in FR soils while SRB soils contained the most abundant nosZ copy number.  The gene copy number of 16S rRNA genes, presumably indicating total bacterial size, ranged from 8.9 x 108 to 6.9 x 109. The nirK and nirS genes were PCR amplified, cloned, and sequenced from DNAs extracted from soils  of FR, AG, and SBR site.  Most sequences from the soils were not closely related to previously observed genes, indicating that these soils contained novel nirK and nirS sequences.  Unique community structures were observed at each site, suggesting that the land use has effected on the development of denitrifying bacteria.
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