Isotope fractionation during ammonium uptake by marine microbial assemblages

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“…Furthermore, concentrations of ammonia and nitrate were negatively associated with the numbers of bacteria (Figures 3, 4). These findings are in agreement to those reported by Tezuka [53] and Hoch et al [54] who stated that addition of carbon diminished inorganic nitrogen due to increasing uptake of NH4+ by bacteria. Zero water exchange ponds using carbon source enabled the control of the inorganic nitrogen accumulation through a balanced ratio of carbon to nitrogen in the feed [20,55,56].…”

Phytoplankton and macrophyte contributions to littoral food webs in the Galician upwelling estimated from stable isotopes

“…Low fractionation of isotopes would imply rapid use of limiting elements, as expected in microbial food webs (Hoch et al 1994). Alternatively, bacteria consuming inorganic nitrogen while recycling organic carbon would provide food sources for consumers that are relatively less enriched in 15 N than the original phytoplankton or macrophyte materials (Altabet 1988, Keil & Fogel 2001.…”

Organic matter pathways to zooplankton and benthos under pack ice in late winter and open water in late summer in the north-central Bering Sea

“…In the northern Bering Sea, it appears that microbial cells or their products are consumed by the abundant macrofauna, producing urea which is hydrolyzed to NH 4 + , which in turn is taken up by bacteria (Blackburn 1987, Lomstein et al 1989 , with a resulting increase of δ 15 N in residual materials (Wada 1980). In experiments with natural assemblages of marine bacteria, mean fractionation of NH 4 + during uptake by bacteria was -10 ‰, ranging from -5 to -20 ‰ depending on the δ 15 N of the source DIN pool (Hoch et al 1994). Thus, if surface deposit-feeders ingested foods derived from bacteria that had assimilated DIN, they would show smaller enrichment in 15 N relative to sediments than would be expected if they fed on the bulk pool of sediment PON.…”

“…These patterns suggest 2 alternatives. First, nitrogen might have been limiting, so that copepods assimilated nitrogen with little isotopic discrimination (Hoch et al 1994, Waser et al 1999). However, nitrogen limitation seems unlikely, because during late winter 2001, when our zooplankton were collected, primary production was very low, inorganic nitrogen levels were high (Clement et al 2004), and C:N ratios of SPOM in most of the water column were <10.4 (Fig.…”