Monday, November 13, 2006 - 2:45 PM

Effect of Carbon Source and Availability on the Amount and Partitioning of Gaseous Denitrification Losses.

Michelle N. Miller1, Bernie Zebarth1, Karen M. Gillam1, Catherine E. Dandie1, David Burton2, Claudia Goyer1, and Jack T. Trevors3. (1) Agriculture and Agri-Food Canada, 850 Lincoln Road, P.O. Box 20280, Fredericton, NB E3B4Z7, Canada, (2) Nova Scotia Agric. College, "Po Box 550, Dept. Of Env. Sci", Truro, NS B2N 5E3, CANADA, (3) University of Guelph, Edmund C. Bovey Building, Guelph, ON N1G 2W1, Canada

Denitrification plays an important role in the global nitrogen cycle and is a principal contributor of nitrous oxide (N2O) to the atmosphere. The objective of this study was to determine the influence of carbon source and availability on the amount and partitioning of gaseous denitrification losses and the size of the denitrifier population. Total denitrification (N2O+N2) and N2O emissions were measured on repacked soil cores using the acetylene inhibition method. Glucose C addition increased the proportion of emissions occurring as N2, as indicated by a decrease in the N2O:(N2O+N2) ratio.  However, when the soil nitrate concentration was simultaneously increased, the ratio also increased. This increase was attributed to nitrate being preferred over N2O as a terminal electron acceptor causing N2O to become the primary product of denitrification. The source of C had a significant effect on the amount of N2O emissions and denitrification.  Availability of C in different C sources was assessed based on cumulative soil respiration during the incubation period. Similar N2O emissions and denitrification were measured for red clover and glucose treatments per unit addition of available C. In contrast, addition of barley straw resulted in significantly lower N2O emissions and denitrification as compared with red clover and glucose per unit addition of available C.  Real-time PCR was used to quantify the total bacterial population, as measured by 16S rDNA.  The denitrifier population was also quantified by measuring the nitric oxide reductase gene (cnorB), which codes for a key enzyme of the denitrification pathway. The source of carbon had a significant effect on the denitrifers, but did not affect the total bacterial population.  Addition of glucose increased the denitrifer bacteria population while red clover and barley straw additions did not affect the same proportion of the denitrifer population.