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Nitrogen cycling in the ocean Deborah Bronk Department of Physical Sciences

Nitrogen cycling in the ocean Deborah Bronk Department of Physical Sciences. bronk@vims.edu. Nitrogen Revolution mid-1990s-present. Nitrification Denitrification/anammox N 2 fixation Anthropogenic N inputs. N. N. N. Why nitrogen is so cool!. SEAWIFs chl a image.

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Nitrogen cycling in the ocean Deborah Bronk Department of Physical Sciences

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  1. Nitrogen cycling in the ocean Deborah Bronk Department of Physical Sciences

  2. bronk@vims.edu

  3. Nitrogen Revolution mid-1990s-present • Nitrification • Denitrification/anammox • N2 fixation • Anthropogenic N inputs N N N

  4. Why nitrogen is so cool! SEAWIFs chl a image

  5. Outline: 1. Types & distribution 2. The Redfield Ratio 3. The nitrogen cycle 4. Liebig’s Law of the Minimum 5. New & regenerated production 6. Is the N cycle in steady state?

  6. Types: Gaseous – N2 gas Dissolved Inorganic: ammonium – NH4+ nitrite – NO2- nitrate – NO3- Organic – DON Particulate – PN (cells & detritus)

  7. Types: Gaseous – N2 gas Dissolved Inorganic: ammonium – NH4+ nitrite – NO2- nitrate – NO3- Organic – DON Particulate – PN (cells & detritus)

  8. Southern California Bight Nitracline Bronk & Ward 2005 DSRI

  9. The Ocean Euphotic zone light - ~little N Aphotic zone no light - lots N

  10. Southern California Bight Nitracline Bronk & Ward 2005 DSRI

  11. TDN - DIN = DON TDN - (NO3- + NO2- + NH4+ )

  12. Karl & Björkman 2002 DOM book

  13. North Pacific Gyre – Particulate Nitrogen (mM) Mahaffey et al. 2008 DSRII

  14. Redfield 1934 James Johnstone Memorial Volume

  15. Read the original papers!

  16. The Redfield Ratio C:N:P = 106: 16: 1 106CO2 + 122H2O + 16HNO3 + H3PO4 (CH2O)106(NH3)16(H3PO4) detritus vs. phyto vs. bacteria?

  17. The Nitrogen Cycle Love, Mulholland, & Bronk 2011

  18. Love, Mulholland, & Bronk 2011

  19. Love, Mulholland, & Bronk 2011

  20. Nitrogen fixation N2 + 8H+ + 8e- + 16 ATP  2 NH3 + H2 + 16 ADP + 16Pi Nitrogenase • “Fixing” broken N2 • Energetically very expensive – N2 has triple bond • Nitrogenase is irreversibly inactivated by oxygen • Most N2 fixers form heterocysts • Requires P, Fe, and trace metals (Mo, Co, V)

  21. N2 fixation N2 N2 Trichodesmium • Two morphological forms • Colonial – 100s cells/trichome and 100s trichomes/colony • Traditionally considered the dominant N fixer in the ocean • Found in tropical and subtropical waters (NOT!)

  22. How do we study the nitrogen cycle? [target] 15N Target Pool Source pool atom % of target Rate = atom % Time of source  

  23. [ ] PN 15N cell 15N2 N2 atom% PN Fixation = Rate atom % N2 Time   

  24. Trichodesmiummystery Non-heterocystous Photosynthesis CO2 O2 N2 fixation N2 NH4+ nitrogenase Temporal or spatial segregation?

  25. cyanophycin granules High resolution-secondary ion mass spectrometry (Nano SIMS) Supports temporal segregation! Finzi-Hart et al. 2009 PNAS

  26. N2 fixation N2 N2 Zehr et al. 2001 Nature Unicellular cyanobacteria that expressed nitrogenase at HOT Montoya et al. 2004 Nature Rates of N fixation by the single cell forms can equal or exceed rates by Trichodemsium

  27. Love, Mulholland, & Bronk 2011

  28. Ammonification N2 * N2 DON NH4+ Phytoplankton * Glibert & Bronk 1994

  29. Ammonification - the conversion of DON or PON to NH4+ Two types: Bacterial - a. Traditional view of bacterial decomposition b. Was considered primary source of NH4+ (Now primary source if believed to be grazers) Photochemical (abiotic!) a. More recently recognized source b. Importance of process is still debated

  30. Love, Mulholland, & Bronk 2011

  31. Nitrification NH4+ ----------------->NO2- -----------------> NO3 Ammonium oxidizers: Nitrite oxidizers: very slow growing faster growing sensitive to light more sensitive to light • Nitrifiers are chemolithoautotrophs. • Maximum rates occur near the base of the • euphotic zone.

  32. Nitrification PN or DON NO2- NH4+ dead cells/detritus ammonification NO3- Nitrifying bacteria - or is it??

  33. Nitracline

  34. Karner et al. 2001 Nature 39% of the picoplankton in the mesopelagic at HOT are archaea.

  35. Könneke et al. 2005 Nature Isolated a marine crenarchaeota that can grow by aerobically oxidizing NH4+ to NO2-. Ingalls et al. 2006 PNAS An isotopic mass balance of radiocarbon signatures of archaeal membrane lipids indicates that 83% of their carbon is obtained autotrophically at depth.

  36. Love, Mulholland, & Bronk 2011

  37. Lost to system Denitrification N2 NO3- NO2- NO N2O nitrate reductase nitrite reductase nitric ox. reductase nitrous oxide reductase • N is used as an electron acceptor, not as a N source • Lots of organisms can reduce NO3- • Fewer can reduce NO2- • All the enzymes are induced by anoxia • NO is very labile and does not accumulate

  38. Denitrification NO2- N2 NO N2O Canonical denitrification (- O2) N2 PN or DON NO3- NO2- NH4+

  39. Love, Mulholland, & Bronk 2011

  40. ANAMMOX ANaerobic AMMonium OXidation + NO2- NH4+ N2 • First described in a wastewater treatment plant in the • Netherlands in 1995. • Oxygen inhibition is reversible. • Thandrup & Dalsgaard (2002) published the first marine • data (sediment study)

  41. Look to other disciplines

  42. N2 ANNAMOX N2 N2 PN NO3- NO2- NH4+ NO2- N2 NO N2O

  43. + NO2- NH4+ N2 N2 NO3- NO2- NO N2O Canonical denitrification? OR Anammox?? obligate anaerobic autotrophs facultative anaerobic heterotrophs

  44. Love, Mulholland, & Bronk 2011

  45. What’s the best way to make a living in a given place? Reaction Energy yield (kcal) Aerobic respiration 686 Denitrification 545 (-O2) Nitrification NH4+ oxidation 66 NO2- oxidation 17 N2 fixation -147

  46. BREAK You see nitrite (NO2-) produced in the water. Design a tracer experiment to determine which process is producing it.

  47. Uptake and regeneration in the surface ocean

  48. Liebig’s Law of the Minimum (1840) - the resource in smallest supply relative to what the organism needs is the limiting factor. Growth versus biomass

  49. Factor limiting growth rates during summer Moore et al. 2004 GBC

  50. SEAWIFs chl a image

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