Extracellular enzyme activity and uptake of carbon and nitrogen along an estuarine salinity and nutrient gradient

Mulholland, Margaret R.; Lee, Cindy; Glibert, Patricia M.

doi:10.3354/meps258003

Cited by 66 publications

(51 citation statements)

References 47 publications

(87 reference statements)

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“…The phyto C: phyto N ratios of the HAAs at this station demonstrate preferential phyto N incorporation by the bacteria, at this station. Previous studies emphasise the importance of extracellular amino-acid oxidation as a pathway for N incorporation in marine systems (Pantoja and Lee, 1994;Mulholland et al, 2003;Veuger and Middelburg, 2007). In the extracellular amino-acid oxidation pathway bacteria liberate NH 4 þ from amino acids outside their cell walls (Pantoja and Lee, 1994).…”

Section: Methodological Considerationsmentioning

confidence: 99%

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

2012

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Oxygen minimum zones (OMZs) currently impinge upon 41 million km 2 of sea floor and are predicted to expand with climate change. We investigated how changes in oxygen availability, macrofaunal biomass and retention of labile organic matter (OM) regulate heterotrophic bacterial C and N incorporation in the sediments of the OMZ-impacted Indian continental margin (540-1100 m;. In situ pulse-chase experiments traced 13 C: 15 N-labelled phytodetritus into bulk sediment OM and hydrolysable amino acids, including the bacterial biomarker D-alanine. Where oxygen availability was lowest ([O 2 ] ¼ 0.35 lmol l À 1 ), metazoan macrofauna were absent and bacteria assimilated 30-90% of the labelled phytodetritus within the sediment. At higher oxygen levels ([O 2 ] ¼ 2-15 lmol l À 1 ) the macrofaunal presence and lower phytodetritus retention with the sediment occur concomitantly, and bacterial phytodetrital incorporation was reduced and retarded. Bacterial C and N incorporation exhibited a significant negative relationship with macrofaunal biomass across the OMZ. We hypothesise that fauna-bacterial interactions significantly influence OM recycling in low-oxygen sediments and need to be considered when assessing the consequences of global change on biogeochemical cycles.

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Section: Methodological Considerationsmentioning

confidence: 99%

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

2012

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“…The uptake of DON by phytoplankton is poorly understood (Mulholland et al, 2003) so we set the half saturation constant for uptake by phytoplankton at 20 M, which allows phytoplankton to take up some DON but restricts it from being their dominant nitrogen source. Phytoplankton use DIC in combination with nutrients at a fixed C:N ratio for production (Anderson and Pondaven, 2003).…”

Section: Phytoplanktonmentioning

confidence: 99%

“…This formulation allows phytoplankton cells to take up ammonium and labile DON preferentially, with nitrate uptake inhibited in the presence of significant concentrations of ammonium Harrison et al, 1996) and labile DON. DON uptake by phytoplankton was included in this model because recent research has shown that DON can be a significant nitrogen source (up to 50%) for phytoplankton (Fan et al, 2003;Mulholland et al, 2002Mulholland et al, , 2003. The maximum attainable daily growth rate of large phytoplankton, P , was calculated using an exponential temperature function (Bissinger et al, 2008;Eppley, 1972).…”

Section: Phytoplanktonmentioning

confidence: 99%

“…doi: 10.1016/j.ecolmodel.2010.12.014 2000). Some phytoplankton also have the ability to take up DOM to supplement their metabolic needs (Mulholland et al, 2003). Photochemical processes, through UV excitation, directly and indirectly remove and transform DOM (Mopper and Kieber, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…DOM can also potentially form gels that may aggregate to form particulate organic matter (POC) (Verdugo et al, 2004) which may sink out of surface waters. As in other temperate systems, the rate and magnitude of these sources and sinks varies on a seasonal basis as changes in light, temperature, and freshwater flow affect the environment (Apple et al, 2006;Bronk et al, 1998;Jonas and Tuttle, 1990;Lomas et al, 2002;Malone et al, 1991;Mulholland et al, 2003;Shiah and Ducklow, 1994b;Wommack et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

Keller

Hood

2011

Ecological Modelling

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a b s t r a c tIn this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.

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Quantifying nitrogen assimilation rates of individual phytoplankton species and plankton groups during harmful algal blooms via sorting flow cytometry

Kang

Kudela

Gobler

2017

Limnology & Ocean Methods

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While 15N‐labeled nitrogen (N) compounds have been used to quantify N uptake rates by plankton communities for decades, accurately ascribing those rates to individual populations or species has been a challenge. Here, we apply sorting flow cytometry combined with species‐specific immuno‐detection of a harmful alga, Aureococcus anophagefferens, to contrast the nutritional ecology of this alga with co‐occurring picoplankton (picoeukaryotes, cyanobacteria, heterotrophic bacteria) during brown tides. The method was iteratively refined to yield close agreement (85–101%) between plankton community 15N uptake quantified via traditional filtration and this novel sorting method. Sorting of plankton revealed that the δ15N values of A. anophagefferens and phycocyanin‐containing cyanobacteria were more enriched (∼ 10‰) than the values of other picoeukaryotes and heterotrophic bacteria that decreased to < 0‰ after A. anophagefferens abundance declined, suggesting that these plankton utilized isotopically lighter nitrogen sources (e.g., recycled nutrients or fertilizer). A. anophagefferens utilized multiple forms of nitrogen (e.g., nitrate, ammonium, urea) during blooms and their uptake rates of ammonium and urea were highest during blooms. However, A. anophagefferens urea uptake rates on a per cell basis were fivefold faster than all other groups, affirming the nutritionally strategic uptake of urea to fuel brown tides. This study presents a novel approach to successfully sort a single algal species from a plankton community for the purpose of assessing nitrogen uptake and highlights a promising and powerful approach for investigating and contrasting the nutritional ecology of bloom‐causing species and co‐occurring plankton populations during harmful algal blooms.

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Extracellular enzyme activity and uptake of carbon and nitrogen along an estuarine salinity and nutrient gradient

Cited by 66 publications

References 47 publications

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

Quantifying nitrogen assimilation rates of individual phytoplankton species and plankton groups during harmful algal blooms via sorting flow cytometry

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