BITÖK
Bayreuther Institut für Terrestrische Ökosystemforschung
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Stief, P; Schramm, A; Altmann, D; De Beer, D: Temporal variation of nitrification rates in experimental freshwater sediments enriched with ammonia or nitrite, FEMS Microbiology Ecology, 46, 63-71 (2003)
Key words: freshwater sediment, nitrogen cycle, nitrification, microsensor, microcosm incubation
Abstract:
Two freshwater sediments (organic-poor and organic-rich) that contained their distinct natural microbial community were incubated in experimental microcosms with either NH4+ or NO2- in the overlying water. Microsensor measurements revealed the thin oxic surface layer as a site of initially high rates of nitrification, i.e. O2, NH4+, and NO2- consumption, and NO3- production. Unexpectedly, during the subsequent four-week incubation NH4+ consumption decreased in both sediment types and NO2- consumption decreased in the organic-rich sediment. In the organic-rich sediment O2 consumption and NO3-- production paralleled these decreases, i.e. the reduced NH4+ and NO2- consumption rates were most probably due to the reduced activity of nitrifiers. Our microsensor data imply factors other than the often suggested competition between nitrifiers and heterotrophs for NH4+, NO2- or O2 as causes for the loss of nitrification activity. We hypothesize that experimental manipulations (e.g., removal of macrofauna, redistribution of particulate organic matter, permanent nutrient enrichment) rendered the performance of the microbial community unstable. It is thus recommendable to restrict experiments in such commonly used model systems to the period of highest stability.
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