Nitrogen and phosphorus cycling in the ocean

Transcription

1 Nitrogen and phosphorus cycling in the ocean Deborah A. Bronk Department of Physical Sciences Outline: 1. The Redfield ratio 2. Liebig s Law of the Minimum 3. The nitrogen cycle 4. The phosphorus cycle 5. New & regenerated production The Redfield Ratio C:N:P = 106: 16: 1 106CO 2 122H 2 O 16H H 3 PO 4 (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) detritus vs. phyto vs. bacteria? Liebig s Law of the Minimum (1840) the resource in smallest supply relative to what the organism needs is the limiting factor. colimitation biochemical or community Ex. biochemical P & Zn limitation Ex. community Si and diatoms Arrigo 2005 Nature

2 Factor limiting growth rates during summer Nitrogen Revolution mid1990spresent N N N Nitrification Denitrification/anammox N 2 fixation Anthropogenic N inputs Moore et al GBC Love et al. In press

3 A plea and a warning! Inorganic nitrogen gas (N 2 ) ammonium (NH 4 ) nitrate ( ) nitrite ( 2 ) Types of nitrogen Organic urea amino acids proteins humic substances more later. Hewson et al ISME TDN DIN = DON TDN ( 2 NH 4 ) Karl & Björkman 2002 DOM book

4 Southern California Bight Phytoplankton Bronk & Ward 2005 DSRI The Ocean light ~no N Phytoplankton no light lots N

5 Production can be defined as new or regenerated based on the source of the nitrogen that fueled it. New nitrogen NH 4 Regenerated nitrogen Dugdale & Goering 1967 L&O N 2 Nitrogen fixation N 2 8H 8e 16 MgATP! 2 NH 3 H 2 16 MgADP 16P i Nitrogenase Fixing broken N 2 Energetically very expensive Nitrogenase is irreversibly inactivated by oxygen Most N 2 fixers form heterocysts

6 N 2 N 2 fixation N 2 N 2 fixation N 2 Trichodesmium N 2 Colonial, nonheterocystous diazotroph Two morphological forms Found in tropical and subtropical waters Traditionally considered the dominant N fixer in the ocean Zehr et al Nature Unicellular cyanobacteria that expressed nitrogenase at HOT Montoya et al Nature Rates of N fixation by the single cell forms can equal or exceed rates by Trichodemsium N 2 Nitrification Nitrification NH 4 > 2 > Ammonium oxidizers: very slow growing sensitive to light Nitrite oxidizers: faster growing more sensitive to light 3 NH 2 4 PN Nitrifying bacteria or is it?? Nitrifiers are chemolithoautotrophs. Maximum rates occur near the base of the euphotic zone.

7 Karner et al Nature 39% of the picoplankton in the mesopelagic at HOT are archaea. Könneke et al Nature Isolated a marine crenarchaeota that can grow by aerobically oxidizing NH 4 to 2.? Ingalls et al PNAS An isotopic mass balance of radiocarbon signatures of archaeal membrane lipids indicates that 83% of their carbon is obtained autotrophically at depth. N 2 Denitrification Denitrification Lost to system important trace gases 3 2 N 2 O N 2 nitrate reductase nitrite reductase nitric ox. reductase nitrous oxide reductase O 2 2 NH 4 PN 2 N 2 O N 2 Canonical denitrification N is used as an electron acceptor, not as a N source Lots of organisms can reduce Fewer can reduce 2, and nitrite reductase is very labile All the enzymes are induced by anoxia is very labile and does not accumulate

8 N 2 N 2 N 2 ANAMMOX ANaerobic AMMonium OXidation NH 2 4 N 2 2 N 2 NH 4 PN First described in a wastewater treatment plant in the Netherlands in Oxygen inhibition is reversible. 2 N 2 O N 2 Canonical denitrification? OR Anammox?? What s the best way to make a living in a given place? NH 2 4 N 2 obligate anaerobic autotrophs 3 2 N 2 O N 2 Reaction Aerobic respiration 686 Energy yield (kcal) Denitrification 545 (O 2 ) Nitrification NH 4 oxidation 66 2 oxidation 17 N 2 fixation 147 facultative anaerobic heterotrophs

9 Gruber In press N in the Marine Env. The Redfield Ratio Big Picture Phosphorus Cycle C:N:P = 106: 16: 1 106CO 2 122H 2 O 16H H 3 PO 4 (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) Paytan & McLaughlin 2007 Chem. Reviews

10 Phosphorus Dissolved inorganic phosphorus (DIP) Orthophosphate H 3 PO 4 <> H 2 PO 4 <> HPO 4 2 <> PO 4 3 phosphoric acid dihydrogen phosphate hydrogen phosphate phosphate Polyphosphates Solubable reactive phosphorus (SRP) P that reacts with a molybdate solution. Includes primarily HPO 4 2 (~87%), PO 4 3, and some reactive organic species. Paytan & McLaughlin 2007 Chem. Reviews Factor limiting growth rates during summer Moore et al GBC Gruber, In press, N in the Marine Env.

11 If nitrogen is queen, phosphorus is king! The domain shift hypothesis Flip Froelich Karl et al DSRII Uptake and regeneration in the surface ocean

12 New nitrogen NH 4 Regenerated nitrogen New production over appropriate spatial and temporal scales equals export flux. Eppley & Peterson 1979 Nature PON

13 fratio = fratio = New production New Regenerated Production uptake NH 4 uptake C:N PON Tomorrow C:N POC

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