Cascading trophic effects on aquatic nitrification: experimental evidence and potential implications

Abstract

Experiments, using natural plankton collected from a eutrophic site in Saginaw Bay, Lake Huron (USA) and from a hypereutrophic wetland of southern Lake Erie (USA), were conducted to test the hypothesis that bacterivory can control aquatic nitnfication rates. The dynamics of nitrogen and protists in these experiments revealed a consistent pattern: an increase in concentrations of nitrates due to oxidation of NH,' always followed the collapse of bacterivorous nanoplankton populations. This collapse was, in turn, caused by predation pressure of larger ciliates and metazooplankton. Experiments, using enrichment batch cultures maintained at near-ambient concentrations of NH,', indicated that bacterivorous protists can inhibit nitnfication directly by reducing bacterial numbers and indirectly by promoting bacterial aggregation. The latter experiments also suggest that feeding strategies of microbial grazers, e.g. suspension-feeding Spumella sp. versus surface-feeding Bodo saltans, may determine their grazing impacts on nitrifiers. Finally, ingestion rates of fluorescently labeled nitrifying bacteria (FLNB) by the natural planktonic assemblage from Saginaw Bay demonstrated that nanoflagellates were able to efficiently prey on low concentrations of FLNB. Our study suggests that previously neglected trophic factors may be of potential importance for mediating nitrification rates in the pelagic environment.

Forming the primary nitrite maximum: Nitrifiers or phytoplankton?

“…Last, future studies need to consider the possibility of trophic interactions as a control on nitrification rates. Research in coastal regions has clearly shown the importance of both ''mutualistic'' microbial associations (e.g., Clark and Schmidt 1966;Steinmuller and Brock 1976;Jones and Hood 1980) and trophic cascades (e.g., Verhagen and Laanbroek 1992;Lee and Welander 1994;Lavrentyev et al 1997). Culture studies with mixed cultures of AOBs and other heterotrophic bacteria are indeed mutualistic, with both NH þ 4 oxidation rates and heterotrophic growth rates increasing when grown together, possibly due to the shuttling of organic metabolites between organisms (e.g., Clark and Schmidt 1967a,b;Jones and Hood 1980).…”

Stratification of the microbial community inhabiting an anchialine sinkhole

“…Within Bundera Sinkhole, photosynthetic primary production is apparently limited to within the top 15% of the water column, but the sinkhole still supports a rich and diverse community of macro-and microorganisms (Yager & Hunphreys 1996, Humphreys 1999. Chemoautotrophic organisms such as sulphuroxidising and nitrifying bacteria can contribute up to 100% of primary production (Sarbu et al 1996) and represent the trophic base (Lavrentyev et al 1997) of subterranean habitats. Our findings indicate that specific microbial populations, including chemoautotrophic groups, can be highly stratified within the water column of anchialine sinkholes, with some populations only present within restricted zones delineated by local water chemistry.…”

Determinacion del flujo de agua para la biorremediacion en sistemas recirculados acuaculturales utilizando tapetes microbianos construidos

“…Sin embargo, eso suele permitir la presencia de procesos de mixotrofía o heterotrofía de manera simultánea y conlleva un eficiente reciclaje y utilización de nutrientes (Lavrentyev et al, 1997;Allen et al, 2001). En la Tabla 2 se presentan los principales taxa aeróbicos obligados autotróficos asociados a los tapetes microbianos algales, su concentración y proporción relativa.…”