Record Details
Contributions of ammonia-oxidizing bacteria and archaea to nitrification in forest soils
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Contributions of ammonia-oxidizing bacteria and archaea to nitrification in forest soils |
| Names |
Lu, Xinda
(creator) Myrold, David D. (advisor) |
| Date Issued | 2014-06-05 (iso8601) |
| Note | Graduation date: 2014 |
| Abstract | Prior to 2005, ammonia oxidation, the first step of nitrification, was thought mediated mainly by ammonia-oxidizing bacteria (AOB). However, the discovery of Thaumarchaeota carrying the genes coding for the ammonia monooxygenase (AMO) enzyme led to the discovery that ammonia-oxidizing archaea (AOA) also contribute to nitrification. Despite the uptick in studies on nitrification following the recognition of AOA, the relative importance and the contribution of AOA and AOB in different ecosystems, and the factors controlling their abundance and activity, have not been well understood. Because nitrogen (N) cycling is mediated by microbes and controls the net primary productivity in forests, and nitrification is the rate controlling step in N cycling, it is important to have a better understanding of nitrification in forest ecosystem, especially the abundance and contribution of AOA and AOB in forest soils. The objective of this study was to determine nitrification activity and nitrifier abundance in forest soils. I wanted to know: (i) if the inclusion of red alder influences the distribution, total nitrification activity, and relative contribution of AOA and AOB to nitrification; (ii) if pH and substrate concentration influence the distribution and activity of ammonia oxidizers, and if so, (iii) what is the relationship between these two factors and nitrification. The study selected soils from stands of red alder (Alnus rubra Bong.) and Douglas-fir (Pseudotsuga menziesii Mirb. Franco) at three sites in Oregon (Cascade Head, the H.J. Andrews, and McDonald Forest) that had a soil pH range of 3.9 to 5.7. The abundances of AOA and AOB were investigated using quantitative PCR (qPCR) by targeting the amoA gene. Nitrification activity was evaluated by nitrification potential in a slurry assay and nitrification rate in whole soil. Activity of AOA and AOB was differentiated by using octyne, which inhibits the AMO enzyme in AOB but not AOA. Nitrification activity and octyne-resistant activity (AOA) were significantly higher at Cascade Head than at the H.J. Andrews and McDonald Forest and greater in red alder compared with Douglas-fir soils. Whole soil nitrification rate was stimulated by high NH₃ concentration (10 mmol kg⁻¹ soil) addition but not by low NH₃ concentration (1 mmol kg⁻¹ soil). At the high concentration of NH₃, both AOA and AOB responded, and nitrification was highest at McDonald Forest, followed by Cascade Head and the H.J. Andrews. There was strong evidence that soil pH was an important factor controlling AOA but not AOB abundance, and the AOA to AOB ratio decreased with increasing soil pH. Collectively, the data indicated that nitrification was mainly driven by AOA in acidic forest soils (pH < 5). |
| Genre | Thesis/Dissertation |
| Access Condition | http://creativecommons.org/licenses/by-nc-nd/3.0/us/ |
| Topic | Nitrification |
| Identifier | http://hdl.handle.net/1957/48980 |
