Institute of Food and Agricultural Sciences (IFAS) Biogeochemistry of Wetlands SiScience an dAd App litilications

Carbon Cycling Processes

Wetland Biogeochemistry Laboratory Soil and Water Science Department University of Florida

Instructor K. Ramesh Reddy [email protected]

6/22/20086/22/2008 WBL 1 1

Institute of Food and Agricultural Sciences (IFAS) Carbon Cycling Processes

CO2 OM

CH4

6/22/2008 WBL 2

1 Carbon Cycling Processes

LtLecture O Otliutline

™ Introduction ™ Major components of carbon cycle ™ Organic matter accumulation ™ Characteristics of organic matter ™ Decomposition processes ™ Regulators of organic matter decomposition ™ Greenhouse gases ™ Summary

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Carbon Cycling Processes

Learning Objectives

™ Describe major components of carbon cycle ™ Develop an understanding of the chemical composition of plant litter and soil organic matter ™ Long-term accumulation of organic matter ™ Describe the role of enzymes and microbial communities involved in decomposition ™ Determine organic matter turnover ™ Indentify the role biogeochemical controls and regulators ™ Understand the global significance of carbon cycle ™ Draw a carbon cycle and identify storages and fluxes within and between soil and water column

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2 Oxidation States of Carbon

[[]+4] [0] CO 2 C6H12O6

[-4]

CH4

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Carbon Reservoirs [1014 kg]

™ Atmospheric CO2 7 ™ Biomass 4.8 ™ Fresh water 2.5 ™ Marine 5-8 ™ Soil organic matter 30-50

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3 Soil Organic Matter [SOM]

™ Undecayed plant and animal tissues ™ Partially decomposed material ™ Soil biomass

Sources of SOM ™ External: Particulate (inputs) ™ Internal: detrital material (macrophytes, algal mats, roots)

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Detrital Plant Biomass

Grazers CO2 microorganisms Aerobic Detritus Decomposition

Peat Water table Water Burial Anaerobic

Compaction

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4 Carbon Cycle UV

CO2 CO2 CH4 Decomposition/leaching

Decomposition/leaching

- Litter Microbial DOC HCO3 Import biomass Export

- Peat Microbial DOC HCO3 Decomposition biomass CH4 leaching Decomposition/leaching 6/22/2008 WBL 9

Organic Matter

¾ Storages ¾ Outputs ¾ Soil organic matter ¾ Greenhouse gases ¾ Plant detritus/litter ¾ Nutrient export ¾ Dissolved organic matter ¾ Ecological/Environment ¾ Microbial biomass al Significance ¾ Transformations ¾ Carbon sequestration ¾ Microbial respiration ¾ MthMethanogenes is ¾ Global warming ¾ Water quality ¾ Ecosystem productivity

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5 Net Primary Productivity 2 [g/m - year] [Craft, 2001] Bog 380-800 Marsh 500 -1100 Riverine 400-1150 Fresh tidal 500-1600 Brackish 600-1600 Salt 950-2000 Mangroves 600-1200

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Carbon Accumulation in Wetlands [g C/m2 year]

Alaska - Sphagnum 11-61 Finland - Sphagnum - Carex 20-28 Ontario - Sphagnum bog 30-32 Georgia - Taxodium 23 Florida - Cladium 70-105

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6 Organic Matter Accumulation 0 Organic matter accumulation

10

1964 marker Soil Depth [cm] 20

Cs-137 Activity 6/22/2008 WBL 13

A. Detritus attached to plant

B. Detritus detached from plant

C. Decomposed Water detritus from detritus previous year

Soil D. Organic matter and nutrient accretion Plant Soil Organic Detritus A B C Matter Decay continuum 6/22/2008 WBL 14

7 Decay Continuum

Live plant CO 2 CH4 Plant standing dead

Litter layer

Surface peat Microbial decomposers

Buried peat 6/22/2008 WBL 15

Carbon Accumulation in Wetlands

™ Potential energy source (reduced carbon, electron donor ™ Long-term storage of nutrients, heavy metals,,gp and toxic organic compounds ™ Major component of global carbon cycles

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8 Carbon Forms

™ Particulate orgg()anic carbon (POC) ™ Microbial biomass carbon (MBC) ™ Dissolved organic carbon (DOC) ™ Dissolved inorganic carbon (DIC)

™ CO2 + H2O = H2CO3 - + ™ H2CO3 = HCO3 + H - 2- + ™ HCO3 = CO3 + H

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Chemical constituents of organic matter

‹ Non Humic compounds: ‹ Carbohydrates (Simple sugars) ‹ Monosaccharides: glucose. ‹ Polysaccharides: Starch, Cellulose, and Hemicellulose ‹ Proteins ‹ Lipids etc

‹ Phenolic compounds: ‹ Lign in (branc he d ran dom po lymer o f p heny l propano id un it ) ‹ Tannins (heterogeneous groups of phenolic compounds)

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9 Organic Matter (Plant and Soil)

• Water soluble components [<10%] – Sugars, amino acids and fatty acids • Cellulose [15-60%] • Hemicellulose [10-30%] • Lignin [5-30%] • Proteins [2-15%] • Lipids and Waxes [1-8%] • Ash (mineral) [1-13%]

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Cellulose

β-D-glucosidic bond

H OH CH OH CH2OH 2

H O H H O O H H H H OH H OH O OH H H H O H

OH OH H CH2OH H

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10 Lignin

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Soil Organic Matter [SOM]

SOM

Extract with Alkali [alkali-soluble] Humin Treat with Acid [alkali-insoluble]

Humic Acid Fulvic Acid [acid-insoluble] [acid-soluble]

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11 Fulvic Acid

• More ‘O’ and less ‘C’. • MW 1000 -30,000. • Less advanced stage of decomposition. • More COOH group per unit mass. • Functional group acidity (11. 2 mol/kg). • Alkali and acid soluble.

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Humic Acid

• More ‘C’ and less ‘O’. • MW 10,000 -100,000. • Advanced stage of decomposition. • Less COOH group per unit mass. • Functional group acidity (6.7 mol/kg). • Alkali soluble.

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12 Available Carbon Pool ƒ Represents small but biologically active fraction of DOC ƒ Immediately available for microbial utilization ƒ Extremely small in C-limited system ƒ Rapid turnover ƒ May not be directly measurable ƒ Affects short-term community metabolism

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Microbial Biomass

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13 Microorganisms [Percent wet weight]

• 70% water ‰ Total weight of • Macromolecules actively growing cell • 15% protein of Escherichia coli • 3% polysaccharide • 2% lipids Wet wt = 9.5 x 10-13 g • 5% RNA Dt2810Dry wt = 2.8 x 10-13 g • 1 % DNA • 1 % Inorganic ions • 3 % others 6/22/2008 WBL 27

Microbial Decomposers ™Typically 1-5% of total C mass in soil ™PtfthttProcess most of the ecosystem net production ™Principal transformers of organic carbon ™Recycle carbon and nutrients in recalcitrant biopolymers ™Regulate energy flow and nutrient retention

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14 Techniques to Measure MICROBIAL BIOMASS

Direc t ce ll coun t : a bun dance Lipid based : live microbial biomass

CHCl3 Fumigation-extraction based: estimate of Carbon Metabolic activity based: Enzyme activities

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MICROBIAL COMMUNITY STRUCTURE

™ Pure culture approach ™ Microscopy ™ Community level physiological profile (CLPP): Substrate utilization: BIOLOG ™ Measurement of cellular component (physiological status, functional groups):PLFA ™ Methods based on nucleic acids analysis (abundance, diversity and phylogeny of organisms): gene specific analysis (16S rDNA, DGGE, TGGE, Trflp)

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15 MICROBIAL BIOMASS [Site = WCA-2A - Everglades]

10 9 8 7 6 LITTER 5 0-10 cm 4 3 10-30 cm 2 1 0 0246810 Distance from Inflow, km 6/22/2008 WBL 31

MICROBIAL NUMBERS [MPN/g soil] [Site = WCA-2A - Everglades] Substrate Eutrophic Oligotrophic Lactate 9.3 x 105 9.2 x 103 Acetate 2.3 x 105 3.6 x 103 Propionate 4.3 x 105 9.2 x 103 Butyrate 43x104.3 x 105 <30x10< 3.0 x 103 Formate 2.3 x 105 < 3.0 x 103

Hector et al. 2003

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16 Detrital Matter Leaching

Complex Polymers Cellulose; Hemicellulose; Lignin Proteins; Lipids and waxes

End product

Monomers Electron Sugars;Amino acids Bacterial acceptors Fatty acids Cell

End products 6/22/2008 WBL 33 + energy

Extracellular Enzymes

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17 Extracellular Enzymes • An extracellular enzyme is involved in transformation or degradation of polymeric substances external to cell membrane. – Enzyme can be bound to the cell membrane or are Periplasmic space periplasmic (ectoenzyme) Bacterial cell (Chrost,1990) – Enzyme occurs free in the water or adsorbed to surface other than its producers e.g., detrital particles or clay Detrital/clay material material (extracellular enzyme) •Most of these are hydrolases

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Enzymes

• Cellulose degradation – Exocellulase - Cellulose – B-glucosidase - Cellobiose • Hemicellulose degradation – Exoxylanase - Xylan – B-xylosidase - Xylobiose • Lignin degradation – Phenol oxidase - Lignin and Phenols

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18 Enzyme – Catalyzed Reaction

E + S E S E + P

S = Substrate E = Enzyme P = Product

All enzymes are proteins – amino acid polymers

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Reactions of Enzymes

2- 2- R-O-PO3 + H2O R-OH + HO-PO3 alkaline phosphatase

- + 2- R-O-SO3 + H2O R-OH + H + SO4 arylsulfatase

R-O-glucose + H2O R-OH + glucose β-glucosidase

casein + H2O tyrosine protease

phenolics + O2 quinones phenol oxidase

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19 Inhibition of enzyme activity Humic acid-Enzyme complex Humic acid Active Enzyme + E E

2+ 2+ 2+ Ca Ca Ca Ca2+ Ca2+ + E Ca2+ + E Ca2+ Ca2+ Ca2+

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Measurement of Enzymes

• Spectroscopic – p-nitrop heno l p hosp hate (p NPP) • Fluorescence – Methylumbelliferyl phosphate (MUF) – Enzyme Labeled Fluorescence (ELF)

APase P P

MUF-P MUF Pi

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20 β Glucosidase Activity -1 h

-1 100

50 -nitrophenol g p

0 g u Oxygen Nitrate Sulfate Bicarbonate E h (mV) 618 214 -145 -217 pH 4.5 7.6 7.5 6.5

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β Glucosidase Activity [Everglades --WCAWCA--2A]2A] 4 impacted

) February transitional

-1 2

ity unimpacted h

v 1 - 0 4 May 2

nitrophenol g nitrophenol 0 p-

-Glucosidase Acti 4

g AtAugust D - (m B 2

0 Detritus 0-10 cm 10-30 cm 6/22/2008Wright and Reddy, 2001 WBL 42

21 Pheno oxidase Activity [Everglades --WCAWCA--2A]2A] 5 Wright and Reddy, 2001

) 4 y 1 May - t 3

min 2

-1 1 0

5 August impacted 4 transitional le [DQC]g

ol Oxidase Activi ol Oxidase unimpacted o 3 n 2 (um Phe 1 0 Detritus 0-10 cm 10-30 cm DQC = dihydroindole quinone carboxylate 6/22/2008 WBL 43

Microbial Activity

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22 Detrital Matter Leaching

Complex Polymers Cellulose; Hemicellulose; Lignin Proteins; Lipids and waxes

Reduced product

Monomers Electron Sugars;Amino acids Bacterial acceptors Fatty acids Cell

End products 6/22/2008 WBL 45 + energy

Organic Matter Decomposition IL DEPTH IL

SO Decreasing energy yield

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23 Metabolism • Catabolism • Anabolism • Types of energy source • Light … Phototrophs • Inorganic … Lithotrophs • Organic …. Heterotrophs • Oxidation of organic compounds • Fermentation • Respiration

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Chemolithotrophy

™ Inorganic compound as energy source

™eg. H2S, Hydrogen gas, Fe(II) , and NH3 ™ Source of carbon for biosynthesis cannot be organic

therefore use CO2 and hence are autotrophs ™ Hydrogen oxidation ™ Sulfur oxidation ™ Ferrous iron oxidation ™ Annamox ™ Nitrification

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24 Phototrophy • Photosynthesis is conversion of light energy into chemical energy.

• Most phototrophs are autotrophs ( use CO2 as sole Carbon source).

OXYGENIC PHOTOTROPHS ANOXYGENIC PHOTOTROPHS

Carbon Carbon H2O ADP CO2 H2S CO2 ADP hυ S0 hυ

1/2O2 (CH2O)n ATP 2- SO4 (CH2O)n ATP

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Metabolism Catabolism Energy sources: Waste products: Organic, inorganic, OiiOrganic, inorgan ic light

Cell biomass

Nutrients: Carbon sources: N, P, K, S, Fe, Organic, CO 2 Mg, ... Anabolism

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25 Pathways for Oxidation of Organic Compounds RESPIRATION: Molecular oxygen (aerobic) or other oxidant (Anaerobic) serves as external electron acceptor FERMENTATION: RdRedox processes occur in th e absence of any external electron acceptor

- CO2, NO2 , reductant Glucose Fe(II), H2SO

oxidationERIA Reduction T BAC - oxidant O2, NO3 , CO2 + H2 Fe(III), SO4

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Metabolism

Assimilative metabolism bacteria (biomass)

Dissimilative Metabolism (energy ) Respiration Fermentation

Aerobic Anaerobic Anaerobic (Oxygen as ( Inorganic, metal as Organic compounds electron acceptor) electron acceptors) as electron acceptors High energy yield Low energy yield 6/22/2008 WBL 52

26 Aerobic Respiration Detrital Matter Enzyme Complex Polymers Hydrolysis Monomers Cellulose, Hemicellulose, Sugars, Amino Acids PtiProteins, Li LiidWpids, Waxes, LiiLignin Fatty Acids

Uptake

Bacterial Cell

Glycolysis Glucose Pyruvate Substrate level phosphorylation

TCA Cycle

CO2 CO2 Acetyl Co A

- O2 O2 + e ATP Oxidative phosphorylation

6/22/2008 WBL 53 H2O

Monomers Sugars, Amino Acids Nitrate Respiration Fatty Acids

Uptake

Glucose Glycolysis

TCA Cycle Pyruvate Substrate level Products: CO 2 Acetate phosphorylation CO2, H2O, N , N O, 2 2 NO - + e- Uptake Organic Acids nutrients 3 Lactate [acetate, propionate, butyrate, lactate, alcohols, H2, and CO2] ATP Nitrate Reducing Bacterial Cell Fermenting Bacterial Cell - NO3 Terminal reductase enzyme (nitrous oxide reductase)

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27 Monomers Sugars, Amino Acids Iron Respiration Fatty Acids Uptake

Glucose Glycolysis

TCA Cycle Pyruvate Substrate level Products: CO 2 Acetate phosphorylation CO2, H2O, 2+ Fe , Fe3+ + e- Uptake Organic Acids nutrients Lactate [acetate, propionate, butyrate, lactate, alcohols, H2, and CO2] ATP

Fe3+ Iron Reducing Bacterial Cell Fermenting Bacterial Cell

Terminal reductase enzyme (ferric reductase)

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Fermentation Organic compound Bacterial Cell

Oxidation

Oxidized Organic compounds [Pyruvate] Electron Reduction carriers

RdReduce d Organic compounds [Ethanol]

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28 Monomers Sulfate Sugars, Amino Acids Fatty Acids

Respiration Uptake

Glucose Glycolysis Oxidative phosphorylation TCA Cycle Pyruvate Substrate level CO2 phosphorylation

, nutrients Acetate 2- 2- - Uptake Organic Acids SO4 + e O, S Products: 2 Lactate [acetate, propionate, butyrate, H lactate, alcohols, H , and CO ] , Substrate level phosphorylation 2 2 2 ATP CO Sulfate Reducing Bacterial Cell Fermenting Bacterial Cell

2- SO4

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Methanogens

™Archaea… not bacteria

™ H2 is electron donor and CO2 is electron acceptor and reduced to CH4 (autotrophic, chemolithotrophy) - 131kJ/mol ™ Respiration, not fermentation ™ Some other substrates that can yield electrons are: ™Hydrogen ™methanol ™Formate

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29 Methanogens

™Hydrogenotrophic methanogens : use H2 (as electron donor) and CO2 ™Acetotrophic methanogens: oxidation of

acetate results in CO2 and CH4.

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Methanogenesis Monomers Sugars, Amino Acids Fatty Acids

Fermenting Bacteria Uptake

CO2 + CH4 Acetate Substrate level phosphorylation Acetate Lactate [Acetotrophic methanogens] + Glucose H H2 Glycolysis , nutrients 4 Pyruvate Acetate CH CO + H CO2 + H2 Substrate level 4 2 2 Acetogenesis O, CH Products: phosphorylation 2 Oxidative phosphorylation , H

2 [Acetogens] [Hydrogenotrophic methanogens] Organic Acids CO [acetate, propionate , butyrate, lactate, alcohols] H2 H2 CO2 CH4 H2 + CH3-OH Fermenting Bacteria [Methyl substrate utilizers]

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30 Other Terminal Electron Acceptors

Inorganic Terminal Electron Acceptors Heavy metals as electron acceptors e.g. • Chromat e C r(VI) Æ Chromi um C r(III) 3- 3- • Arsenate (AsO4 ) Æ Arsenite (AsO3 ) 2- 2- • Selenate (SeO4 ) Æ Selenite (SeO3 ) Æ inorg. Se

Organic Terminal Electron Acceptors Fumarate Æ succinate Trimethyl amine oxide (TMAO) Æ trimethlamine(TMA) Dimethyl sulfoxide (DMSO) Æ Dimethyl sulfide Reductive dechlorination

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EVERGLADES - WCA-2A 2.0 1.8 TION

) 1.6 A 1 -

d 1.4 -1 1.2 1.0 0.8 0.6 BIC RESPIR g CO2-C

O 040.4 m ( 0.2

AER 0.0 0 5 10 15 20 25 30 35 40 MICROBIAL BIOMASS C (mg g-1) 6/22/2008 WBL 62

31 Aerobic Respiration

700 Impacted Unimpacted ion, Everglades, FL t 600 Everglades, FL 500 Talladega, AL Houghton Lake 400 marsh, MI 300 Salt marsh, LA Belhaven, NC 200 mg/kg day mg/kg Lake Apopka marsh, FL y=-1036+200 ln(x) 2 ygen consump 100 Prairie pp,othole, ND R =0.84

x Crowley, LA

O 0 0 500 1,000 1,500 2,000 2,500 3,000 3,500 Dissolved organic C, mg/kg

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Nitrate Respiration

60 Houghton Lake Impacted marsh, MI Everglades, FL

n, 50 y Salt marsh, LA 40 Unimpacted Everglades, FL Talladega, 30 Prairie pothole, ND AL

20 Lake Apopka marsh, FL

mg N/kg mg N/kg da y=-64+14 ln(x)

Denitrificatio Belhaven, NC 10 2 Crowley, LA R =0.91 0 0 500 1,000 1,500 2,000 2,500 3,000 3,500 Dissolved organic C, mg/kg

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32 Microbial Respiration [Everglades Soils] 60 ate

ons Sulfate reducing f 50 Denitrifyyging i ] 1 - -1 y = 0.41x + 1.1 y = 0.33x + 1.3 40 r2 = 0.89; n = 24 2 hour r = 0.88; n = 24 1 - -1 30

[mg kg [mg 20 ducing condit enitrifying/Sul e r D 10

0 10 20 30 40 50 60 Aerobic [mg kg--11 hour--11] 6/22/2008 WBL 65

Microbial Respiration [Everglades Soils] 10 ions

t y = 0 .13x + 0 .3 8 CO ] 2 2

1 r = 0.85, n = 24 - -1 6 hour 1 - -1 4 nogenic condi [mg kg [mg a 2 y = 0. 08x - 020.2 CH4 r2 = 0.70, n = 24 Meth 0 10 20 30 40 50 60 Aerobic, [mg kg--11 hour--11] 6/22/2008 WBL 66

33 Anaerobic vs Aerobic Respiration 0.7 L 0.6 L A L L IRATION IRATION ) 0.5

P d L A L 0.4

0.3 L A (mg C/g AL L 0.2 A ROBIC RES L E A A y = 0. 324x + 0 .02 0.1 SSA A 2 SS r = 0.94 SSS SS ANA 0 0 0.5 1.0 1.5 2.0 AEROBIC RESPIRATION (mg C/g d) 6/22/2008 WBL 67

Regulators

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34 Regulators of Organic Matter Decomposition ™ Substrate quality ™ carbon to nitrogen ratio or carbon to phosphorus ratio of the substrate ™ Temperature ™ Availability of electron acceptors ™ Microbial populations

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Regulators of Organic Matter Decomposition and Nutrient Release Death/senescence Plant N and P

CO2 CH4 Flux

Soil Organic Matter Bioavailable Accumulation Decomposition N and P N and P

Elect ron Hydrology Nutrients Rainfall Acceptors

Evapotranspiration External Loading

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35 Substrate Quality Debusk and Reddy. 1998. Soil Sci. Soc. Am. J. 62:1460-1468

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14C-(Lignin) Lignocelluloses

Carex

Spartina Spartina Carex

Red mangrove Red mangrove

Benner et al. 1985. Limnol. Ocenogr. 30:489-499

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36 14C-(Polysaccharide) Lignocelluloses

Spartina Carex

Spartina Carex

Red mangrove Red mangrove

Benner et al. 1985. Limnol. Ocenogr. 30:489-499

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Detrital Decomposition in Wetlands Okeechobee Drainage Basin

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37 Detrital Decomposition in Wetlands Okeechobee Drainage Basin

0.4

0.3 constant, k/day e Rat

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Detrital Decomposition in Wetlands Okeechobee Drainage Basin y te constant, k/da a R

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38 Relative Biodegradability of Substrates [Aerobic] [Time - half life, days]

Ð Sugars 0.6 days Ð Hemicellulose 7 days Ð Cellulose 14 days Ð Lignin 365 days

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Plant Litter Decomposition

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39 Substrate Quality 60

Lignin Cellulose 50

40

30

% Dry mass 20

10

0 Cattail Sawgrass Litter Peat Peat (0-10 cm) (10-30 cm)

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A. Live Tissue [Lignin] [ LCI = 0.14-0.17] LCI = [Lignin + Cellulose]

B. Detritus attached to thlhe plant [LCI = 0.23-0.29]

C. Detritus [LCI = 0.6] Water

0-10 cm soil [LCI = 0.73] Soil

10-30 cm soil [LCI = 0.81] 6/22/2008 WBL 80

40 Decomposition-Hydrology

6/22/2008 WBL 81

Decomposition-Hydrology

) 600 -1

ay 500 d

-2 400

-C m 300 2

200

100

k (mg CO 0 -40 -30 -20 -10 0 10 20 30 Water Depth (cm)

41 Alternate Aerobic/Anaerobic Conditions

Anaerobic 3.75 Aerobic )

-1 3.00

2.25

1.50 -C evolved (mg g 2 -64 -32 -16 8 8 2 4 8 4 2 6

0.75 2 2 O 6 3 1 1 1 2- 8- 4- C

0 0 0 1 2 4 81632 Number aerobic/anaerobic cycles

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Decomposition of Detrital Plant Tissue [Lake Apopka Marsh] 0.16 0.12 Saggitaria ay

d 0080.08 k/ 0.04 0 0.16

0.12 Typha y Summer 0.08 Winter k/da 0.04 0 Decomposition N-release P-release 6/22/2008 WBL 84

42 Microbial Respiration – Soil Temperature 300 ) n 1 - o hr 200 -2

100 (mg C m Soil respirati

0 0 5101520 Soil temperature at 10 cm (°C)

Arrhenius Equation kAk = A e - E/RTE / RT k = Reaction Rate Constant ; A = Arrhenius coefficient ; E = Activation Energy ; R = Gas constant ; and T = Temperature (K)

T T k1 = k2 1 2

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43 Microbial Respiration – Soil Temperature

10

8

10 6 Q 4

2

0 0 510152025 30 35 Temperature (°C)

Microbial Activity [Site: Water Conservation 2A] )

-1 250 h DiDrained conditi ons -1 y = 0.07x + 52 200 R2 = 0.58

150

100

roduction (mg C kg Flooded conditions P 50 2 y = 0.06x + 26 R2 = 0.72 CO 0 0 500 1000 1500 2000 Total Phosphorus (mg P kg-1)

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44 Lake Apopka Marsh 16 3.5 14 3 ) mg/L)

12 L 2.5 10 N = 0.13 C + 1.56 R2 = 0.77; n = 94 2 8 6 1.5

4 P = 0.025 C + 0.56 1 2

monium-N ( R = 0.68 ; n = 94 2 0.5 (mg/ luble P o m S

A 0 0 0 20 40 60 80 100 120

Dissolved (inorganic + CH4 )-C (mg/L)

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Soil Organic Matter

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45 Plant Detritus Decomposition Detrital plant tissue or Carbon loading

CO2 Residue Microbial [lignin] biomass

HUMUS

Humus: Total of the organic compounds in soil exclusive of undecayed plant and animal tissues, their “partial decomposition” products and the soil microbial biomass 6/22/2008 WBL 91

Functional Groups

¾ Carboxylic COOH ¾ Phenoloic OH

¾ Hydroxyl OH

¾ Amine NH2 ¾ Sulfhydrl SH

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46 Functional Groups

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Functions of Organic Matter

• Source of nutrients for ppglant growth. • Source of energy for soil microorganisms. • Source of exchange capacity for cations. • Provides long-term storage for nutrients. • Strong adsorbing agent for toxic organic compounds. • Complexation of metals.

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47 Variable Charge on Soil Organic Matter

COOH COO- COO- OH -H+ OH -H+ O-

O + H+ O + H+ O

Acidic pH Alkali pH

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Complexation with Metals

• Metal ions that would convert to insoluble precipitates are maintained in solution. • Influences the bioavailability of metals. • Some organic complexes with metals may low solubility.. complexation with humic acids. • Inhibits enzyme activity. • Plays a significant role in transporting metals from one ecosystem to another.

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48 Complexation with Metals

COOH COO M OH O + M2+ + 2H+ O O

Acidic pH Alkali pH

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Greenhouse Gases

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49 6/22/2008 WBL 99

Methane Flux

400 ay) d

2 300 /m 2 200

Methane Flux 100 (mg C-CO

0 0 2 4 6 8 10 12

2 Net Ecosystem Productivity (g C-CO2/m day)

6/22/2008 WBL 100

50 Methane Production and Oxidation

O2 CH4

CH4

Water

O2 + CH4 CO2

CO2 Soil O2 + CH4 Organic CH4 Matter 6/22/2008 WBL 101

Carbon Cycle in Wetlands UV

CO2 CO2 CH4 Decomposition/leaching

Decomposition/leaching

- Litter Microbial DOC HCO3 Import biomass Export

- Peat Microbial DOC HCO3 Decomposition biomass CH4 leaching Decomposition/leaching 6/22/2008 WBL 102

51 Carbon Cycling Processes Summary

™ Carbon is important for living systems because it can exist in a variety of oxidation states (-4, 0, +4) and serves as a source of electrons for microbial processes. ™ Most decomposition of organic matter is driven by oxygen, but less efficient electron acceptors are used in anaerobic processes ™ Humic substances are divided into three major groups: Fulvic acid (acid and base soluble); Humic acid (acid insoluble and base soluble); Humin (acid and base insoluble) ™ Detrital matter is broken down into compppylex polymers (cellulose, proteins, lipids, lignin). Enzymes break these polymers into simple monomers (sugars, amino acids, fatty acids) ™ Organic mater is a source (short term and long term storage) of nutrients for plants and soil microbes ™ Enzymatic hydrolysis is the rate limiting step in SOM decomposition

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Carbon Cycling Processes Summary

™ Decomppgyqy,position is regulated by substrate quality, electron acceptors (who, how many), limiting nutrients, and temperature ™ Functions of Organic Matter: Source of nutrients for plant growth; source of energy for soil microorganisms; provides long-term storage for nutrients; strong adsorbing agent for toxic organic compounds; complexation of metals ™ Aerobic decomposition results in the production of oxidized species - 2- 4+ 3+ (CO2. H2O, NO3 , SO4 , and Mn and Fe oxides), while the anaerobic decomposition results in the production of reduced species + 2+ 2+ (H2, fttfatty acid idNHs, NH4 , N2, N2OlfidCHO, sulfides, CH4, Fe andMd Mn ) ™ Wetlands contain approximately 15 to 22% of the terrestrial carbon and one of the major contributor to the global methane flux , which accounts for approximately 20 to 25% of global methane to atmosphere

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http://wetlands.ifas.ufl.edu

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