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Title: The effect of major environmental factors on archaeal and bacterial ammonia oxidisers in soil
Author: Bello, Marcus
ISNI:       0000 0004 7228 724X
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2018
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Nitrification is the conversion of ammonia to nitrate via nitrite and is performed by ammonia oxidising archaea (AOA), complete ammonia-oxidiser (comammox) and ammonia and nitrite oxidising bacteria (AOB and NOB). The aim of this study is to examine the effect of ammonia concentration, temperature, drought and inhibitors on activity of AOA and AOB using soil microcosms and cultures. Ammonia concentration in soil increases during drought due to the reduced soil water content and, with desiccation stress or a combination of both factors, may result in reported greater inhibition of AOA than AOB during drought. The independent effects of both matric potential and initial ammonium concentration on AOA and AOB amoA abundances and nitrate production were studied in soil microcosms. AOA were more susceptible to increased desiccation stress than AOB, irrespective of initial soil ammonium concentration, and AOA cultures were more sensitive than AOB to osmotic stress induced by different concentrations of NaCl or sorbitol. This may represent an additional niche differentiating factor between AOA and AOB in soil. The effect of temperature and supply of high levels of inorganic ammonium on ammonia oxidation by AOA and AOB were also investigated in soil microcosms. Activity and growth of AOA and AOB were observed in soil amended with high ammonium concentration with increasing temperature, suggesting that AOA can contribute to nitrification in highly fertilised soil, particularly at 25 oC. Inhibition of AOA by simvastatin was investigated in culture and in soil. Simvastatin selectively inhibited AOA in both systems and soil microcosm studies provided evidence for oxidation of ammonia by AOB at low ammonium concentration. Generally, the results show the benefits of combining soil microcosm and culture-based approaches in soil microbiology. The findings advance our understanding of the influence of ammonium supply, temperature and osmotic stress on soil nitrification and its role in controlling the availability of ammonium-based fertilisers for plant uptake.
Supervisor: Not available Sponsor: University of Aberdeen ; TETFund Nigeria
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nitrification ; Soils ; Nitrification inhibitors