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Understanding Dissolved Organic Matter: Composition, Microbial Diversity, and Carbon Preservation

Explore the complex relationship between dissolved organic matter (DOM), microbial diversity, and carbon preservation. Learn about the composition of DOM, its effects on microbial adaptation and evolution, and the factors that influence the oceanic inventory of organic carbon.

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Understanding Dissolved Organic Matter: Composition, Microbial Diversity, and Carbon Preservation

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  1. Dissolved Organic Matter- what is inside the black box? What is the relationship between organic matter composition, microbial diversity & production? How is microbial metabolism coupled to organic matter structure? How does DOM affect microbial adaptation & evolution? What sets the ocean inventory of organic carbon, and why is so much organic carbon preserved in seawater? Why do organic nitrogen and phosphorus accumulate in nutrient limited regions of the surface ocean where they are most needed, but disappear in the mesopelagic ocean where they are not needed?

  2. DOC sampling is hard to do… Isolation of DOM by ultrafiltration Separation based on size 1 nm pore @ 1 kD Selects for HMW fraction about 30-35% TOC Membrane effects what Is collected Some salts collected too!

  3. DOC sampling filter (1 nm) sample concentrate (> 1000 MW) pump filtrate (< 1000 MW)

  4. Ultrafiltration high molecular weight DOM (HMWDOM) membrane filter >1000 D DOM fraction 30-35% DOC < 1000 D DOM fraction 65-70% DOC

  5. Final product 30-35% of total DOC

  6. DOM analysis by Nuclear Magnetic Resonance spectroscopy

  7. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter (HMWDOM) Frequency Abundance

  8. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter (HMWDOM) Frequency Different types of carbon resonate at different frequencies Area is proportional to the amount of carbon Abundance 200 150 100 50 0 ppm

  9. 1H, 31P, 15N - NMR spectra of HMWDOM 1H 15N 31P Clark et al L&O 2001

  10. 13CNMR spectra of HMWDOM from the Atlantic and Pacific Sargasso Sea NPSG 3 m 3 m

  11. 13CNMR of marine phytoplankton* Fragilariopsis cylindrus Phaeocystis antarctica *Adina Paytan, 2005

  12. 13CNMR of plankton tows Hedges et al GCA 2001

  13. 13CNMR of HMWDOM in different aquatic environments North Pacific Ocean Great Salt Lake Leenher et al., (2004) Biogeochem. 69, 125-141 Andrews Creek, RMNP McKnight et al. (1997) Biogeochem. 62, 99-124

  14. HMWDOM in the deep sea Sargasso Sea NPSG 3 m 3 m 2500 m 1800 m

  15. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter

  16. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter COOH CONH (10%)

  17. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter OCO (12%) COOH CONH (10%)

  18. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter HCOH (55%) OCO (12%) COOH CONH (10%)

  19. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter HCOH (55%) OCO (12%) C/N = 15 +/- 3 COOH CONH (10%) CHx (10%)

  20. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter HCOH (55%) OCO (12%) C/N = 15 +/-3 HCOH OCO = 4-5 COOH CONH (10%) CHx (10%)

  21. HMWDOC, what could it be? From our knowledge of cell biochemicals… Proteins C/N = 4, CHx(O):CON = 3 Carbohydrates C maybe N HCOH:OCO = 5 Lipids C only CHx:COOH = 18 CHx:COH = 30

  22. HMWDOC, what could it be? From our knowledge of cell biochemicals… Proteins C/N = 4, CHx(O):CON = 3 Carbohydrates C maybe N HCOH:OCO = 5 Lipids C only CHx:COOH = 18 CHx:COH = 30 ……..looks to be mostly (50-70%) carbohydrate !

  23. Carbohydrate 50-70% of HMWDOC 200 150 100 50 0 Spectral and chemical analyses of HMWDOC -O- -O- 13CNMR Acid hydrolysis

  24. Carbohydrate 50-70% of HMWDOC R F A X Gl M Ga 200 150 100 50 0 Spectral and chemical analyses of HMWDOC Acid hydrolysis followed by Monosaccharide analyses yields 7 major neutral sugars that represent 10-20% of HMWDOC in surface water 13CNMR Acid hydrolysis

  25. NMR and carbohydrate analyses of deep sea HMWDOC monosaccharide distribution surface relative % deep relative %

  26. Can we use the 14C of pure sugars to determine If they are part of the reactive or nonreactive fraction of DOC? reactive DOC 14C=DIC “nonreactive” DOC 14C = DOC(deep)

  27. Radiocarbon analyses of HMWDOC carbohydrates Sample Hawaii NPSG DIC 72+7‰ (n=4) 89+7‰* Glucose 47, 58 79 Galactose 67 103 Mannose 65 99 Xylose 52, 58 94 Arabinose 63 ND Fucose 49, 52 69 Rhamnose 40, 57 57 Average 56+6‰ 89+13‰ *data from Ellen Druffel

  28. Can 14C in sugars constrain the turnover time of The “semi-reactive” fraction of DOC? Assume the concentration of reactive DOC is at steady state,and that it produced each year with a 14C value equal to DIC. Each year a fraction of the sugars are non-selectively removed and the 14C value for the remainder is calculated.

  29. O = -C-N -C-NH2 What else is in HMWDOC ? 15N NMR (90-98%) Amide-N Amino-N (2-10%)

  30. proteins -C-N- -C-N- amino sugars O O CH3CONH CH3CONH What else is in HMWDOC ? 15N NMR Amide-N Amino-N

  31. Is a large fraction of HMWDOC and HMWDON from amino sugars? 15N NMR 1HNMR Amide-N Acetate

  32. Is a large fraction of HMWDOC and HMWDON from amino sugars? 15N NMR 1HNMR Amide-N Acetate HNOCCH3 HNOCCH3

  33. HNOCCH3 HNOCCH3 Is a large fraction of HMWDOC and HMWDON from amino sugars? Amide-N Amide-N Amino-N HNH HNH

  34. CH3CONH CH3CONH Is a large fraction of HMWDOC and HMWDON from amino sugars? 15N 1H acid HNH HNH + CH3COOH

  35. Composition and cycling of HMWDOM Most of the carbon (75%) is carbohydrate Half the N is from aminosugars, about 10% is from proteins The sugar/aminosugar fraction is the “semi-labile: DOC that accumulates in surface waterthis may fuel about 50% of microbial production in surface waters. Why does it accumulate? Surface HMWDOM

  36. What is the composition of Non-reactive DOC in the deep ocean (1800 m Pacific)

  37. HO -C-N- -C-N- O O O O O O O -C-N- -C-N- CH3 CH2 CH2 -C-N- -C-N- Non-reactive DOM Semi-reactive DOM Very reactive DOM Mostly polysaccharides Biopolymers… 80-90% of cell C-N-P Don’t really Know Humic substances? Free amino acids Simple sugars Urea…etc. 10-20% of cell C-N-P

  38. Non-reactive DOM Semi-reactive DOM Very reactive DOM Humic substances Proteins Polysaccharides Biopolymers… 80-90% of cell C-N-P Free amino acids Simple sugars Urea…etc. 10-20% of cell C-N-P Concentration = 40 µM 25-40 µM 100 nm-1µM (?) Inventory = 650 GT C 30-50 GT C 0.1- 1 GT C 14C= -400 to -600‰ 14C= +70-90‰ (?) 14C= +70-90‰ Annual flux = 0.1 GTC Moderate to large ? Large

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