Wednesday, November 7, 2007 - 11:10 AM
289-7
Denitrifier Population Dynamics Under Potato Production in Relation to Nitrous Oxide Emissions and Denitrification.
Claudia Goyer1, Cathy E. Dandie1, David Burton2, Bernie J. Zebarth1, Sherri L. Henderson1, and Jack T. Trevors3. (1) Potato Research Centre, Agriculture and Agri-Food Canada, 850 Lincoln Rd, Fredericton, NB E3B 4Z7, Canada, (2) CANADA, Nova Scotia Agric. Coll., Nova Scotia Agric. College, Po Box 550 Dept. Of Env. Sci, Truro, NS B2N 5E3, CANADA, (3) Environmental Microbiology Department, University of Guelph, 50 Stone Rd East, Guelph, ON N1G 2W1, Canada
Nitrous oxide (N2O) is the most important greenhouse gas from agricultural crop production and is associated with the process of denitrification in humid environments. Despite considerable research on understanding the magnitude and controlling factors for N2O emissions, there is limited information on denitrifier population dynamics within agricultural soils. This study quantified spatial and temporal variation in denitrifier population dynamics in a podzolic soil cropped to potato. Soil samples were collected on ten sampling dates from early spring to late fall, and for different row locations (rhizosphere, bulk soil in potato hill and furrow) during the crop growth period. Denitrifiers were quantified based on real-time PCR amplification of functional gene sequences. Functional genes targeted included the cnorB gene of Pseudomonas mandelii and closely-related spp. (cnorB-P) and Bosea-Bradyrhizobium-Ensifer (cnorB-B), nirK and nosZ gene targeting broad groups of bacterial denitrifiers. Denitrification rate (acetylene-blockage method) and N2O emissions (static chamber method) were measured in the potato hill and furrow on each sampling date. The cnorB-P, cnorB-B and nosZ gene bearing populations from the hill were lower before planting in mid-May, were increased during the period from planting until mid-July, then slowly decreased over the remainder of the monitoring period. The exception was the broad nirK denitrifier community which declined slowly over the duration of the monitoring period. The magnitude of the changes in denitrifier abundance was generally small: up to 2.7-fold for the broad nirK and nosZ denitrifier groups and the specific cnorBB guild. In contrast, the cnorBP population showed up to ~5-fold change over time and spatial location. Populations were higher in the rhizosphere and potato hill than in the furrow. Denitrifier abundance in this system appears to be uncoupled from denitrification activity, with changes in denitrifier abundance more likely to be affected by carbon availability and other environmental (i.e. soil temperature) factors.