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The relationship between carbon dioxide and oxygen exchange during nitrification.
Thesis information
Author:
Kettlewell, Bubby.;Advisor(s):
Layzell, David B.Degree:
Ph.D.School:
Queen's University at Kingston (Canada).Year:
2005Full Abstract
The utility of gas exchange as an indicator or indirect measure of biological process in complex ecosystems was explored through monitoring soil nitrification response to N amendments. Instrumentation and measurement systems were developed for the simultaneous analysis of CO2 and O2 exchange of soil. After providing (NH4)2SO4 amendment to a sandy loam, O2 consumption more than doubled while CO 2 evolution decreased more than model predictions. The respiratory quotient (RQ) dropped from a basal ratio of 1.1 to below 0.4. During nitrification in silt loam and sandy loam at three moisture levels, CO2 evolution increased but less than the O2 uptake. The greatest average O 2 uptake occurred in soils with 60% water filled pore space (WFPS), but maximum O2 uptake occurred at 80% WFPS. Soils with 40% WFPS showed slower response to treatment and no return to basal RQs over the time period. Silt loam with 40% WFPS accumulated the least amount of NO3-N (6.06 mumol N g-1 dry soil) while sandy loam with 40% WFPS accumulated the most (9.89 mumol N g-1 dry soil).;In an effort to develop a noninvasive assay, CO2 and O 2 exchange were used to calculate the flow of reducing energy from NH 4+ oxidation (assuming 4 e- per CO2 or O2), and this value was compared to the soil NO3- pool increase. Despite large gas exchange signatures, gas analysis measurements could not consistently account for the reducing energy associated with the measured NO3- product. However, the rapid change in RQ provided a reliable indicator of process.;Field measurements using a static soil chamber method showed similar, though proportionally less effect on gas exchange from urea amendment to soil. Single point measurements of nighttime atmospheric O2 and CO2 concentration changes were taken as a first step to move the O2 and CO2 measurements to larger scales using micrometeorological methods. Overall, it was concluded that a gas exchange signature is associated with nitrification and therefore there is a potential to use gas analysis as a semi-quantitative measure of process. More studies are needed to adapt the methods for use in the field and at larger scales.
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