CURRENTLY
POSTPONED
By Associate Prof. Nathaniel B. Weston, Department of Geography and the Environment, Villanova University.
Controls on Nitrous Oxide Production in Soils and Sediments: The Role of Stress
The microbial nitrogen cycling processes of denitrification, nitrification, and dissimilatory nitrate reduction to ammonia are contributors to nitrous oxide (N2O) emissions from soils, sediments, and waters to the atmosphere. Denitrification in soils and sediments has been identified as a major source of N2O to the atmosphere. N2O is produced as an intermediate by denitrifiers during the reduction of nitrate (NO3-) or nitrite (NO2-) to dinitrogen gas (N2). N2O is a potent greenhouse gas and is responsible for significant ozone depletion. N2O emission rates and atmospheric concentrations have increased in response to intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Substrate availability (NO3- and organic matter) and environmental factors such as oxygen, temperature, moisture, and pH have been identified as important controls on rates of denitrification, N2O production, and the ratio of N2O to total denitrification (N2O:DNF). We examined the role of changing environmental conditions, or ‘stress,’ in agricultural soils and estuarine sediments, on rates of denitrification, N2O production, and N2O:DNF ratios. Changes in salinity, temperature, moisture, pH, and zinc inhibited rates of total denitrification but increased N2O:DNF ratios. Net N2O production generally increased under moderate levels of stress, though N2O production was inhibited at higher levels of stress in some treatments. These results indicate that stress on the microbial denitrifying community, brought about by changes in physicochemical conditions, can induce higher net N2O production and alter the yield of N2O relative to N2.