Inputs into Microbial Food Chains

Sharp, Jonathan H.

doi:10.1007/978-1-4684-9010-7_5

Cited by 13 publications

(6 citation statements)

References 55 publications

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“…The release of LMW D0I5N was a small percentage (0 to 16 %) of total D0I5N release, suggesting that direct release by phytoplankton was not a n important release mechanism. Furthermore, the low percentages of LMW DO1% release to I5NH,+ uptake ( 2 i 2 %) are consistent with reports from both laboratory and field studies (reviewed by Sharp 1984) which indicate that phytoplankton do not lose much of their recently assimilated organic material under steady state conditions, or under conditions of rapid growth.…”

Section: Time-course Patterns In Don Releasesupporting

confidence: 75%

A 15N tracer method for the measurement of dissolved organic nitrogen release by phytoplankton

Bronk¹,

Glibert²

1991

Mar. Ecol. Prog. Ser.

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ABSTRACT-We present a new method for separation of dissolved organic nitrogen (DON) from dissolved inorganic nitrogen (DIN) in marlne samples which permlts the measurement of DO'*N production during DII5N uptake and regeneration experiments. Ion retardat~on resin was used to separate DI1'N from DOI'N and the isolated D0I5N was subsequently analyzed by mass spectrometry Variat~on in D0I5N atom % enrichment in duplicate samples, determined w~t h the ion retardation column method, was less than 4"0. We also separated the low n~olecular weight (LMW) DO"N from total D015N using ultrafiltration and found the ratio of these variables to b e a useful index in determining what release processes were likely occurring in a given sample. Examples are presented from 2 types of experiments conducted in Chesapeake Bay waters: first, a 6 h time-course of D015N release from both "NH,' and I5NO3-uptake, and second, a series of short-term (0.5 h) release measurements from 15NH,* uptake over the course of a day. In the former, total DO1% release rates resulting from 15NH,* uptake were several-fold higher than those resulting from IsNO3-uptake d u e to extremely low rates of incorporat~on of "NO? into cellular organic material. The release of LMW DOI'N resulting from I5NH,+ uptake decreased from 78 to 21 % of total D0I5N release during the 6 h incubation which suggests that processes other than direct release by phytoplankton (e.g. sloppy feeding, cell lysis) likely became more important as the incubation progressed In the latter expenment, LMW DO'% release was 0 to 16 % of total D0I5N release, which indicates that, in this case, also, processes other than direct release by phytoplankton were dominating the flux of DON from phytoplankton.

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Section: Time-course Patterns In Don Releasesupporting

confidence: 75%

A 15N tracer method for the measurement of dissolved organic nitrogen release by phytoplankton

Bronk¹,

Glibert²

1991

Mar. Ecol. Prog. Ser.

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“…Phytoplankton do not release large amounts of organic matter for bactenal consumption when they are in log phase (Sharp 1984). Our estimates for the Delaware Estuary suggest direct organic loss by phytoplankton of less than 10 % of the fixed carbon (Murphy & Sharp unpubl.).…”

Section: Phytoplankton As Bacterial Substratementioning

confidence: 75%

“…It is interesting to note that our estimates of direct phytoplankton excretion during the spring and summer period give a range of 0.2 to 27 % of the production with an average of 6.9 O/O (Murphy & Sharp unpubl.). Either these are underestimates of organic excretion (as discussed in Murphy & Sharp) or much of the bacterial carbon demand is coming from other carbon sources such as decay of dead phytoplankton cells (see Sharp 1984) or zooplankton influences (grazing losses, zooplankton excretion).…”

Section: Phytoplankton As Bacterial Substratementioning

confidence: 99%

Microbial trophodynamics in the Delaware Estuary

Coffin¹,

Sharp²

1987

Mar. Ecol. Prog. Ser.

114

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ABSTRACT:The relationship between bacteria, phytoplankton and heterotrophlc microflagellates is examined over large spatial and seasonal scales in the Delaware Estuary, USA. The estuary was sampled along the main salinity axis (0 to 30 ppt), from near Philadelphia to the mouth, between February and Auqust 1985. Samples were analysed for bacterial abundance and production, for heterotrophic microflagellate abundance and rate on bacteria, and for phytoplankton production and biomass. Temperature was a major factor that requlated bacteria and microflaqellates. With the exception of cold peridds, bacterla and microflagellates appeared to respond to phytoplankton production During the spring and summer, bacterial production and microflagellate grazing were highest in the lower estuary, where phytoplankton production was also highest. Bacter~al production was on average 23 % of the phytoplankton carbon production. In this area of the estuary grazing on bacteria was h~ghest. Bacterivores grazed 95 % of the bacterial production. Estimates on the carbon flow from phytoplankton to bacteria and subsequently to microflagellates suggest that bacteria and microflagellates do not return lost phytoplankton production to the main phytoplankton-zooplankton food chain in the Delaware Estuary. Instead, it appears that the primary effect of heterotrophic microbes is the mineralization of organic compounds to their inorganic constituents.

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“…We suggest that nutrient-deficient phytoplankton were also contributing to the DFAA flux. Release of DFAA by nutrient-poor phytoplankton has been well documented (reviewed by Sharp 1984). The negative correlations between DFAA and zooplankton biomass imply that DFAA was released mainly during the times of day when copepods were least abundant in near-surface waters (i.e.…”

Section: Discussionmentioning

confidence: 99%

Dependent coupling of inorganic and organic nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary and its regulation by large heterotrophs

Glibert

Garside

Fuhrman

et al. 1991

Limnology & Oceanography

144

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Nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary was studied during a series of four cruises (1985)(1986). During each season we followed the short-term patterns in inorganic (NH,', NO,, and organic (urea and dissolved free amino acids-DFAA) nitrogen uptake and regeneration as plume water aged and became incorporated into ambient coastal water over l-3 d. There was little influence of seasonally changing temperature on inorganic nitrogen uptake rates: the highest specific and absolute hourly rates of uptake occurred in April, when the availability of total N was al a seasonal high; rates were somewhat lower in early and late summer and were lowest in February. NH,+ regeneration rates, on the other hand, were highly correlated with temperature, with the highest rates occurring in late summer. Rates of DFAA uptake were highest in June. Urea contributed up to 70-80% of the total N utilized during winter and summer; in spring most nitrogen uptake was in the forms of NO, and NH,'. The seasonal differences in the patterns of release of dissolved organic N, and the role of zooplankton in mediating this flux, paralleled the patterns previously reported for the release of dissolved organic C in the Chesapeake Bay plume. That is, in winter most organic N release was not grazer mediated, but instead was more likely due to nutrient-deficient phytoplankton. In contrast, in late summer, there seemed to be more dissolved organic N release by grazers, either directly or from "sloppy feeding." At all seasons, in the transition from the bay environment 'to coastal waters, autotrophic populations appeared to become nutrient deficient, and a system dominated by heterotrophic processes rapidly became established.Anthropogenic nutrient input plays an important role in the high productivity and Acknowledgments This research was supported by NSF grants OCE 84-09465 (P.M.G.), OCE 84-07033 (C.G.), OCE84-067 12 (J.A.F.), OCE 84-06700 (M.R.R.), and OCE 87-16909 as part of the MECCAS program. This is Contribution 2220 from the Center for Environmental and Estuarine Studies, University of Maryland, and 9 1008 from the Bigelow Laboratory for Ocean Sciences.We thank Sue Banahan, Robert Ray, Jean Garside, Gary Tilton, Gary Ncwhart, Anne Benbaw, Kathy Ashton, Joe Montoya, and others who assisted with the collection and analysis of the data presented here. We are grateful for the cooperation of the captains and crews of the RV Oceanus and RV Gyre. We are also grateful to Jim McCarthy for assisting in the intercalibration study and to Tom Malone and Hugh Ducklow for providing the phytoplankton and bacterioplankton biomass data.

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Inputs into Microbial Food Chains

Cited by 13 publications

References 55 publications

A 15N tracer method for the measurement of dissolved organic nitrogen release by phytoplankton

A 15N tracer method for the measurement of dissolved organic nitrogen release by phytoplankton

Microbial trophodynamics in the Delaware Estuary

Dependent coupling of inorganic and organic nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary and its regulation by large heterotrophs

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