Phytoplankton and bacterial biomass, production and growth in various ocean ecosystems

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1 Phytoplankton and bacterial biomass, production and growth in various ocean ecosystems Location Bact. Biomass (mg C m -2 ) Phyto. Biomass (mg C m -2 ) BactB: PhytoB BactP (mg C m -2 d -1 ) 1 o Pro (mg C m -2 d -1 ) 1 o Pro: PhytoB (d -1 ) BactP: BactB (d -1 ) 1 o Pro: BactP Sargasso Sea North Atlantic Bloom Subarctic North Pacific Station ALOHA Arabian Sea Average St. dev CV (%)

2 Bacterial biomass, growth and production in the oceans Bacterial biomass is typically % of phytoplankton biomass. In oligotrophic ecosystems, bacterial biomass can exceed phytoplankton biomass. Bacterial production typically ranges ~10-30% of primary production. Bacterial growth rates range 0.1 to 0.5 d -1 (equivalent to doubling times of ~1 to 7 days). Top down pressures control biomass, bottom up factors control growth.

3 CO 2, NH 4+,PO 4 3- DOM Bacterial Biomass Regeneration of nutrients BP ~10-30% PP Higher trophic levels Available to food web

4 Nutrients, biology and stoichiometry

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6 Organic matter production 106 CO HNO 3 + H 3 PO H 2 O (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+138O 2 Consumes CO 2 Consumes nutrients Produces oxygen Aerobic remineralization of organic matter: (CH 2 O) 106 (NH 3 )16H 3 PO O 2 106CO H 2 O +16HNO 3 + H 3 PO 4 Consumes O 2 Produces CO 2 Recycles nutrients

7 Subtropics and tropics: oligotrophic = low nutrient, low biomass. Equatorial upwelling regions: Elevated nutrients (1-10 µm NO 3- ) and biomass (relative to surrounding waters). High latitude: High nutrients (10-30 µm NO 3- ), elevated biomass.

8 Nutrients make things grow

9 Where do ocean nutrients come from? Rivers Air Recycling Deep Sea 1) Deep ocean (physics) 2) Recycling (biology) 3) River runoff (mostly physics) 4) Air (both physics and biology)

10 Physics and biology control primary production Physics light and nutrient availability, wind-driven transport of nutrients Biology N 2 fixation, nutrient uptake, remineralization

11 Physical supply of nutrients to the upper ocean Mixing Upwelling

12 Deep mixing provides nutrients but also reduces amount of light available for growth Nitrate (µmol L -1 ) SHALLOW MIXED LAYER Depth (m) Light Nitrate Light (mol quanta m -2 d -1 ) DEEP MIXED LAYER

13 Nitrogen assimilation Nitrogen is an essential nutrient found in amino acids, protein, and nucleic acids. Nitrogen is assimilated by both autotrophs and heterotrophs. In large areas of the world s ocean, nitrogen limits primary production. Nitrogen in organic matter is reduced; however, most fixed nitrogen in the ocean is oxidized (nitrate) and thus requires reductant for assimilation into biomass.

14 Plankton production is supported by 2 types of nitrogen: 1) new production supported by external sources of N (e.g. NO 3- and N 2 ), 2) recycled or regenerated production, sustained by recycling of N. -Why does this generalization apply to the open sea but not near shore environments?

15 The f-ratio Assumptions: 1) N 2 fixation is low 2) Steady state system 3) Euphotic zone nitrification is low f = VNO 3- / (VNO 3- + N R ) Note N R includes regenerated forms of N uptake (historically thought to include urea and NH 4+ ) Mathematical description linking new production and organic matter export. At steady state, nitrogen input is balanced by nitrogen export. N 2 regenerated NH + 4 NO - 3 new new Biological production export Under steady state (i.e. nitrate input balanced by export/grazing loss), if export is less than input, biomass accumulates. This biomass must eventually be exported to keep the system in steady state. NO 3 - NO 2 - NH 4 + N export

16 Duce et al. (2008) Science 320: About 80% of primary production recycles thru microbial loop a. Inputs of new nutrients (b +c+d) must balance export b

17 DIC (µmol kg -1 ) NO NO 2 - (µmol kg -1 ) Depth (m) PO 4 3- (µmol kg -1 ) Oceanic primary production ~50 PgC yr -1 Oceanic New Production: ~11 PgC yr -1 NO NO 2 - PO 4 3- DIC

18 Not all new nutrients are introduced to the euphotic zone from below Atmospheric deposition (both dry and wet) can form an important source of nutrients. Advection: lateral input of nutrients N 2 fixation

19 N 2 fixation is the primary mode of introducing fixed nitrogen to the biosphere. N 2 fixation converts N 2 to NH 3 ; process is exclusively mediated by prokaryotes Energy expensive to break triple bond in N 2 N 2 + 8H + + 8e + 16 ATP 2NH 3 + H ADP + 16 PO 4 3-

20 Fritz Haber Carl Bosch Haber-Bosch N 2 fixation: 3CH 4 + 6H 2 O 3CO H 2 4N H 2 8NH 3 Requires high temperatures and pressure Provides nitrogen for >30% of the world s food supply.

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22 Fasham et al. (2003)

23 Global estimate of N 2 fixation based on N-DIC drawdown in NO 3 -depleted warm waters is equivalent to 0.8 ±0.3 Pg C yr -1

24 N 2 fixation may also play an important role in controlling nutrient stoichiometry in the sea

25 TDN = 14.57(TDP) NO NO2 - (µmol L -1 ) Nitrogen (µmol L -1 ) TDN : TDP NO3 - : PO4 3- Nearly identical slopes, but different intercepts Phosphorus PO 3-4 (µmol (µmol L -1 ) L -1 ) NO 3- = (PO 4 3- )

26 Duce et al. (2008) Science 320: About 80% of primary production recycles thru microbial loop a. Inputs of new nutrients (b +c+d) must balance export b

27 Organic matter production 106 CO HNO 3 + H 3 PO H 2 O (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+138O 2 Consumes CO 2 Consumes nutrients Produces oxygen Aerobic remineralization of organic matter: (CH 2 O) 106 (NH 3 )16H 3 PO O 2 106CO H 2 O +16HNO 3 + H 3 PO 4 Consumes O 2 Produces CO 2 Recycles nutrients

28 O2 concentration (µmol O2 L-1) Depth (m) N+N O NO3 + NO2 (µmol L ) (CH2O)106(NH3)16H3PO O2 106CO H2O +16HNO3 + H3PO4

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30 Depth (m) 2000 Pacific Atlantic NO NO 2 - (µmol L -1 )

31 Aerobic regeneration of nitrogen Decomposition of organic matter (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2 106CO H 2 O +16HNO 3 + H 3 PO 4 average organic matter composition: 54% protein, 25% carbohydrate, 16% lipid, 4% nucleic acid

32 Aerobic regeneration of nitrogen Complete decomposition of organic matter (CH 2 O) 106 (NH 3 )16H 3 PO O 2 106CO H 2 O +16HNO 3 + H 3 PO 4 Multi-step process. First step is the breakdown of amino acids to NH 4 + (termed ammonification) 2NH O 2 2NO H + + 2H 2 O 2NO 2- + O 2 2NO 3 - These reactions yield energy (but not much )

33 Oxidized N Energy to be gained in oxidation Reduced N (Sarmiento & Gruber, 2006)

34 Nitrification Biological oxidation of NH 3 to NO 3- using oxygen as terminal electron acceptor. Two step process; ammonia oxidation followed by nitrite oxidation; both reactions yield energy. NO 2- serves as an important intermediate; incomplete nitrification also yields N 2 O.

35 Degradation of organic N to ammonium occurs during heterotrophic metabolism. Nitrification is a 2 step process that is mediated by different groups of microbes. The first step (termed ammonium oxidation) oxidizes NH 4+ to NO 2-, and the second step converts NO 2- to NO 3-.

36 Let s look at dissimilatory nitrogen transformations Oxidized N Energy to be gained in oxidation Reduced N (Sarmiento & Gruber, 2006)

37 Denitrification The reduction of NO 3- and NO 2- to N 2 during heterotrophic respiration of organic matter. Occurs predominately in anaerobic or suboxic environments. C 106 H 175 O 42 N 16 P NO 3-106CO N 2 + H 3 PO H 2 O NO 3- and NO 2- are used as terminal electron acceptors during heterotrophic respiration. Removal of NO 3- by this mechanism in the ocean alters the CO 2 : NO 3- : PO 4 3- ratios

38 Oxygen concentrations along the 26.9 kg m -3 isopycnal surface (~500 m in the N. Pacific) Chlorophyll distributions

39 Anaerobic ammonium oxidation (anammox) NH 4+ + NO 2-2N 2 + 2H 2 O Anaerobic ammonium oxidation Major source of N 2 gas (along with denitrification) Anoxic sediments, marine water column, and sewage wastewater Mediated by Planctomyces

40 N input by N 2 Losses of N by fixation denitrification N 2 Atmosphere N 2 N 2 O Photosynthesis Organic Bacterial matter degradation NH + 4 Nitrification NO 2 - NO 3 - Aerobic Suboxic Denitirifcation N 2 O N 2 O Detritus Bacterial degradation NH 4 + N 2