Transcript soils.ifas.ufl.edu

Institute of Food and Agricultural Sciences (IFAS)
Biogeochemistry of Wetlands
Science and Applications
Carbon Cycling Processes
Wetland Biogeochemistry Laboratory
Soil and Water Science Department
University of Florida
Instructor
K. Ramesh Reddy
[email protected]
7/6/2015
7/6/2015
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Institute of Food and Agricultural Sciences (IFAS)
Carbon Cycling Processes
CO2
OM
CH4
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Carbon Cycling Processes
Lecture Outline
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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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Oxidation States of Carbon
[+4]
[0]
CO2
C6H12O6
[-4]
CH4
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Carbon Reservoirs
[1014 kg]
 Atmospheric CO2
 Biomass
 Fresh water
 Marine
 Soil organic matter
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4.8
2.5
5-8
30-50
6
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
microorganisms
CO2
Aerobic
Water table
Detritus
Decomposition
Peat
Burial
Anaerobic
Compaction
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Carbon Cycle
UV
CO2
CO2 CH4
Decomposition/leaching
Decomposition/leaching
Litter
Import
Peat
Decomposition
leaching
Microbial
biomass
DOC
HCO3-
Microbial
biomass
DOC
HCO3CH4
Export
Decomposition/leaching
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Organic Matter
 Storages




Soil organic matter
Plant detritus/litter
Dissolved organic matter
Microbial biomass
 Transformations
 Outputs
 Greenhouse gases
 Nutrient export
 Ecological/Environment
al Significance




 Microbial respiration
 Methanogenesis
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Carbon sequestration
Global warming
Water quality
Ecosystem productivity
10
Net Primary Productivity
[g/m2 - year]
[Craft, 2001]
Bog
Marsh
Riverine
Fresh tidal
Brackish
Salt
Mangroves
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380-800
500 -1100
400-1150
500-1600
600-1600
950-2000
600-1200
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Carbon Accumulation in
Wetlands
[g C/m2 year]
Alaska - Sphagnum
Finland - Sphagnum - Carex
Ontario - Sphagnum bog
Georgia - Taxodium
Florida - Cladium
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11-61
20-28
30-32
23
70-105
12
Organic Matter Accumulation
Soil Depth [cm]
0
Organic matter
accumulation
10
1964
marker
20
Cs-137 Activity
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A. Detritus attached
to plant
B. Detritus detached
from plant
Water
detritus
D. Organic matter
and nutrient
accretion
Soil
Plant
B
C
Detritus A
Decay continuum
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C. Decomposed
detritus from
previous year
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Soil Organic
Matter
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Decay Continuum
Live plant
CO2
CH4
Plant
standing dead
Litter layer
Microbial
decomposers
Surface peat
Buried peat
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Carbon Accumulation in
Wetlands
 Potential energy source (reduced
carbon, electron donor
 Long-term storage of nutrients, heavy
metals, and toxic organic compounds
 Major component of global carbon
cycles
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Carbon Forms
 Particulate organic carbon (POC)
 Microbial biomass carbon (MBC)
 Dissolved organic carbon (DOC)
 Dissolved inorganic carbon (DIC)
 CO2 + H2O = H2CO3
 H2CO3 = HCO3- + H+
 HCO3- = CO32- + 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:


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Lignin (branched random polymer of phenyl propanoid unit)
Tannins (heterogeneous groups of phenolic compounds)
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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
b-D-glucosidic bond
O
H
OH
H
H
OH
H
H
OH
CH2OH
H
H
O
H
O
H
H
O
H
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OH
H
CH2OH
OH
H
H
O
CH2OH
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H
OH
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Lignin
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Soil Organic Matter [SOM]
SOM
Extract with Alkali
[alkali-soluble]
Humin
[alkali-insoluble]
Treat with Acid
Humic Acid
Fulvic Acid
[acid-insoluble] [acid-soluble]
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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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Available Carbon Pool
 Represents small but biologically active
fraction of DOC
 Immediately available for microbial
utilization
 Extremely small in C-limited system
 Rapid turnover
 May not be directly measurable
 Affects short-term community
metabolism
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Microbial Biomass
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Microorganisms
[Percent wet weight]
• 70% water
• Macromolecules
• 15% protein
• 3% polysaccharide
• 2% lipids
• 5% RNA
• 1 % DNA
•
•

Total weight of
actively growing cell
of Escherichia coli
Wet wt = 9.5 x 10-13 g
Dry wt = 2.8 x 10-13 g
1 % Inorganic ions
3 % others
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Microbial Decomposers
Typically 1-5% of total C mass in soil
Process 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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Techniques to Measure
MICROBIAL BIOMASS
Direct cell count : abundance
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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MICROBIAL BIOMASS
[Site = WCA-2A - Everglades]
10
9
8
7
LITTER
6
0-10 cm
5
4
10-30 cm
3
2
1
0
0
2
4
6
8
10
Distance from Inflow, km
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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
4.3 x 105
< 3.0 x 103
Formate
2.3 x 105
< 3.0 x 103
Hector et al. 2003
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Leaching
Detrital Matter
Complex Polymers
Cellulose; Hemicellulose; Lignin
Proteins; Lipids and waxes
End product
Monomers
Bacterial
Cell
Sugars;Amino acids
Fatty acids
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Electron
acceptors
End products
+ energy
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Extracellular
Enzymes
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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 (ectoenzyme)
(Chrost,1990)
– Enzyme occurs free in the
water or adsorbed to surface
other than its producers e.g.,
detrital particles or clay
material (extracellular
enzyme)
Bacterial cell
Periplasmic
space
Detrital/clay material
•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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Enzyme – Catalyzed Reaction
E+S
S = Substrate
ES
E = Enzyme
E+P
P = Product
All enzymes are proteins – amino acid polymers
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Reactions of Enzymes
R-O-PO32- + H2O
R-OH + HO-PO32alkaline phosphatase
R-O-SO3- + H2O
R-OH + H+ + SO42arylsulfatase
R-O-glucose + H2O
casein + H2O
R-OH + glucose
b-glucosidase
tyrosine
protease
phenolics + O2
quinones
phenol oxidase
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Inhibition of enzyme activity
Humic acid-Enzyme
complex
Active
Enzyme
Humic acid
E
+ E
Ca2+
Ca2+
Ca2+
Ca2+
+ E
Ca2+
Ca2+
Ca2+
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Ca2+
+ E
Ca2+
39
Measurement of Enzymes
• Spectroscopic
– p-nitrophenol phosphate (pNPP)
• Fluorescence
– Methylumbelliferyl phosphate (MUF)
– Enzyme Labeled Fluorescence (ELF)
P
MUF-P
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APase
P
MUF
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Pi
40
ug p-nitrophenol g-1 h-1
b Glucosidase Activity
100
50
0
Oxygen Nitrate
E h (mV) 618
214
pH
4.5
7.6
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Sulfate Bicarbonate
-145
-217
7.5
6.5
41
b Glucosidase Activity
B-D-Glucosidase Activity
(mg p- nitrophenol g-1 h-1)
4
[Everglades -WCA-2A]
February
2
impacted
transitional
unimpacted
0
4
May
2
0
4
August
2
0
Detritus
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Wright and Reddy, 2001
0-10 cm
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10-30 cm
42
Pheno oxidase Activity
Phenol Oxidase Activity
(umole [DQC]g-1 min-1)
[Everglades -WCA-2A]
Wright and Reddy, 2001
5
4
3
2
1
0
5
4
3
2
1
0
May
August
Detritus
0-10 cm
impacted
transitional
unimpacted
10-30 cm
DQC = dihydroindole quinone carboxylate
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Microbial Activity
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Leaching
Detrital Matter
Complex Polymers
Cellulose; Hemicellulose; Lignin
Proteins; Lipids and waxes
Reduced product
Monomers
Bacterial
Cell
Sugars;Amino acids
Fatty acids
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Electron
acceptors
End products
+ energy
45
SOIL DEPTH
Organic Matter Decomposition
Decreasing
energy
yield
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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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Phototrophy
• Photosynthesis is conversion of light energy into
chemical energy.
• Most phototrophs are autotrophs ( use CO2 as sole
Carbon source).
OXYGENIC PHOTOTROPHS
H2O
Carbon
CO2
ANOXYGENIC PHOTOTROPHS
ADP
H2S
Carbon
CO2
ADP
(CH2O)n
ATP
hu
hu
1/2O2
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(CH2O)n
S0
ATP
SO42-
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Metabolism
Catabolism
Energy sources:
Organic, inorganic,
light
Waste products:
Organic, inorganic
Cell biomass
Carbon sources:
Organic, CO2
Anabolism
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Nutrients:
N, P, K, S, Fe,
Mg, ...
50
Pathways for Oxidation of
Organic Compounds
RESPIRATION: Molecular oxygen (aerobic) or other oxidant
(Anaerobic) serves as external electron acceptor
FERMENTATION: Redox processes occur in the absence of any
external electron acceptor
reductant
oxidation
BACTERIA
Glucose
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Reduction
oxidant
CO2 + H2
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CO2, NO2-,
Fe(II), H2SO
O2, NO3-,
Fe(III), SO4
51
Metabolism
Assimilative
metabolism
(biomass)
bacteria
Dissimilative
Metabolism
(energy )
Fermentation
Respiration
Aerobic
Anaerobic
(Oxygen as
electron acceptor)
( Inorganic, metal as
electron acceptors)
Organic compounds
as electron acceptors
Low energy yield
High energy yield
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Anaerobic
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Aerobic Respiration
Detrital Matter
Enzyme
Hydrolysis
Complex Polymers
Monomers
Sugars, Amino Acids
Fatty Acids
Cellulose, Hemicellulose,
Proteins, Lipids, Waxes, Lignin
Uptake
Bacterial Cell
Glycolysis
Glucose
Pyruvate
Substrate level phosphorylation
TCA Cycle
CO2
CO2
Acetyl Co A
O2 + e -
O2
ATP
Oxidative phosphorylation
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H2O
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Monomers
Nitrate Respiration
Sugars, Amino Acids
Fatty Acids
Uptake
Glucose
Glycolysis
Pyruvate
TCA Cycle
Products:
CO2, H2O,
N2, N2O,
nutrients
CO2
Substrate level
phosphorylation
Acetate
NO3- + e-
Uptake
Lactate
Organic Acids
[acetate, propionate, butyrate,
lactate, alcohols, H2, and CO2]
ATP
NO3-
Nitrate Reducing Bacterial Cell
Fermenting Bacterial Cell
Terminal reductase enzyme
(nitrous oxide reductase)
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Monomers
Iron Respiration
Sugars, Amino Acids
Fatty Acids
Uptake
Glucose
Glycolysis
Pyruvate
TCA Cycle
Products:
CO2, H2O,
Fe2+,
nutrients
CO2
Substrate level
phosphorylation
Acetate
Fe3+ + e-
Uptake
Lactate
Organic Acids
[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]
Reduction
Electron
carriers
Reduced
Organic compounds
[Ethanol]
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Sulfate
Respiration
Monomers
Sugars, Amino Acids
Fatty Acids
Uptake
Products:
CO2, H2O, S2-, nutrients
Glucose
Glycolysis
Oxidative phosphorylation
Pyruvate
TCA Cycle
CO2
Substrate level
phosphorylation
Acetate
SO42- + e-
Uptake
Lactate
Substrate level phosphorylation
Organic Acids
[acetate, propionate, butyrate,
lactate, alcohols, H2, and CO2]
ATP
Sulfate Reducing Bacterial Cell
Fermenting Bacterial Cell
SO42-
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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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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
Fermenting Bacteria
CO2 + CH4
Acetate
Sugars, Amino Acids
Fatty Acids
Uptake
Substrate level phosphorylation
Acetate
Products:
CO2, H2O, CH4, nutrients
Monomers
[Acetotrophic methanogens]
H+
Lactate
H2
Glucose
Glycolysis
Pyruvate
CH4
CO2 + H2
Acetate
CO2 + H2
Substrate level
phosphorylation
Acetogenesis
Oxidative phosphorylation
[Hydrogenotrophic methanogens]
[Acetogens]
Organic Acids
H2
CH4
H2 + CH3-OH
[acetate, propionate, butyrate,
lactate, alcohols]
H2
CO2
Fermenting Bacteria
[Methyl substrate utilizers]
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Other Terminal Electron Acceptors
Inorganic Terminal Electron Acceptors
Heavy metals as electron acceptors e.g.
• Chromate Cr(VI) 
Chromium Cr(III)
• Arsenate (AsO43-) 
Arsenite (AsO33-)
• Selenate (SeO42-) 
Selenite (SeO32-)  inorg. Se
Organic Terminal Electron Acceptors
Fumarate

succinate
Trimethyl amine oxide (TMAO)  trimethlamine(TMA)
Dimethyl sulfoxide (DMSO)  Dimethyl sulfide
Reductive dechlorination
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AEROBIC RESPIRATION
(mg CO2-C g-1 d-1)
EVERGLADES - WCA-2A
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
MICROBIAL BIOMASS C (mg g-1)
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62
Oxygen consumption,
mg/kg day
Aerobic Respiration
700
600
500
Talladega, AL
400
Salt marsh, LA
300
Houghton Lake
marsh,
MI
Belhaven, NC
200
y=-1036+200 ln(x)
R2=0.84
Lake Apopka marsh, FL
Prairie pothole, ND
Crowley, LA
100
0
Impacted
Everglades, FL
Unimpacted
Everglades, FL
0
500
1,000
1,500
2,000
2,500
3,000
3,500
Dissolved organic C, mg/kg
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63
Nitrate Respiration
Denitrification,
mg N/kg day
60
Houghton Lake
marsh, MI
50
Impacted
Everglades, FL
Salt marsh, LA
40
Unimpacted
Everglades, FL
30
Prairie pothole, ND
20
Talladega,
AL
Lake Apopka marsh, FL
Belhaven, NC
Crowley, LA
10
y=-64+14 ln(x)
R2=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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64
Microbial Respiration
[Everglades Soils]
[mg kg-1 hour-1]
Denitrifying/Sulfate
reducing conditions
60
50
Denitrifying
40
y = 0.41x + 1.1
r2 = 0.89; n = 24
y = 0.33x + 1.3
r2 = 0.88; n = 24
30
20
10
0
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Sulfate reducing
10
20
30
40
50
Aerobic [mg kg-1 hour-1]
WBL
60
65
Microbial Respiration
10
[mg kg-1 hour-1]
Methanogenic conditions
[Everglades Soils]
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8
CO2
y = 0.13x + 0.3
r2 = 0.85, n = 24
6
4
2
y = 0.08x - 0.2
CH4 r2 = 0.70, n = 24
0
10
20
30
40
50
Aerobic, [mg kg-1 hour-1]
WBL
60
66
ANAEROBIC RESPIRATION
(mg C/g d)
Anaerobic vs Aerobic Respiration
0.7
L
L
0.6
L
A
L
0.5
A
0.4
L
L
0.3
0.2
A
S
A
S
SS A
S SS
SS
S
0.1
0
L
0
A
A
L
A
A
AL
L
y = 0.324x + 0.02
r2 = 0.94
0.5
1.0
1.5
2.0
AEROBIC RESPIRATION (mg C/g d)
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Regulators
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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
Soil Organic Matter
Accumulation
N and P
Rainfall
Electron
Acceptors
Hydrology
Evapotranspiration
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Decomposition
Flux
Bioavailable
N and P
Nutrients
External Loading
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70
Substrate Quality
Debusk and Reddy. 1998. Soil Sci. Soc. Am. J. 62:1460-1468
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71
14C-(Lignin)
Lignocelluloses
Carex
Spartina
Spartina
Carex
Red mangrove
Red mangrove
Benner et al. 1985. Limnol. Ocenogr. 30:489-499
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72
14C-(Polysaccharide)
Spartina
Lignocelluloses
Carex
Carex
Red mangrove
Spartina
Red mangrove
Benner et al. 1985. Limnol. Ocenogr. 30:489-499
7/6/2015
WBL
73
Detrital Decomposition in Wetlands
Okeechobee Drainage Basin
7/6/2015
WBL
74
Detrital Decomposition in Wetlands
Okeechobee Drainage Basin
Rate constant, k/day
0.4
7/6/2015
0.3
WBL
75
Detrital Decomposition in Wetlands
Rate constant, k/day
Okeechobee Drainage Basin
7/6/2015
WBL
76
Relative Biodegradability
of Substrates [Aerobic]
[Time - half life, days]




7/6/2015
Sugars
Hemicellulose
Cellulose
Lignin
0.6 days
7 days
14 days
365 days
WBL
77
Plant Litter Decomposition
7/6/2015
WBL
78
Substrate Quality
60
Lignin
Cellulose
% Dry mass
50
40
30
20
10
0
Cattail
7/6/2015
Sawgrass
Litter
WBL
Peat
(0-10 cm)
Peat
(10-30 cm)
79
A. Live Tissue
[ LCI = 0.14-0.17]
LCI =
[Lignin]
[Lignin + Cellulose]
B. Detritus attached
to the 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]
7/6/2015
WBL
80
Decomposition-Hydrology
7/6/2015
WBL
81
k (mg CO2-C m-2 day-1)
Decomposition-Hydrology
600
500
400
300
200
100
0
-40
-30
-20
-10
0
10
Water Depth (cm)
20
30
Alternate Aerobic/Anaerobic
Conditions
Anaerobic
Aerobic
3.00
2.25
2
2-2
1
4-4
0
8-8
32-32
0
16-16
64-64
0.75
128
1.50
128
CO2-C evolved (mg g-1)
3.75
4
8
16
32
0
Number aerobic/anaerobic cycles
7/6/2015
WBL
83
Decomposition of Detrital Plant
Tissue [Lake Apopka Marsh]
k/day
0.16
0.12
Saggitaria
0.08
0.04
k/day
0
0.16
0.12
Typha
0.08
Summer
Winter
0.04
0
7/6/2015
Decomposition
N-release
WBL
P-release
84
Microbial Respiration –
Soil Temperature
Soil respiration
(mg C m-2 hr-1)
300
200
100
0
0
5
10
15
20
Soil temperature at 10 cm (°C)
Arrhenius Equation
k = Ae
- E / RT
k = Reaction Rate Constant ; A = Arrhenius coefficient ;
E = Activation Energy ; R = Gas constant ; and
T = Temperature (K)
k1 = k2
7/6/2015
WBL
T1 T2
86
Microbial Respiration –
Soil Temperature
10
Q10
8
6
4
2
0
0
5
10 15 20 25
Temperature (°C)
30
35
Microbial Activity
CO2 Production (mg C kg-1 h-1)
[Site: Water Conservation 2A]
250
Drained conditions
y = 0.07x + 52
200
R2 = 0.58
150
100
Flooded conditions
50
y = 0.06x + 26
R2 = 0.72
0
0
500
1000
1500
2000
Total Phosphorus (mg P kg-1)
7/6/2015
WBL
88
16
14
12
10
8
6
4
2
0
0
3.5
3
2.5
N = 0.13 C + 1.56
R2 = 0.77; n = 94
2
1.5
P = 0.025 C + 0.56
R2 = 0.68 ; n = 94
20
40
60
80
100
1
0.5
0
120
Soluble P (mg/L)
Ammonium-N (mg/L)
Lake Apopka Marsh
Dissolved (inorganic + CH4 )-C (mg/L)
7/6/2015
WBL
89
Soil Organic Matter
7/6/2015
WBL
90
Plant Detritus Decomposition
Detrital plant tissue
or Carbon loading
Residue
[lignin]
CO2
Microbial
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
7/6/2015
WBL
91
Functional Groups
7/6/2015
 Carboxylic
 Phenoloic
COOH
OH
 Hydroxyl
 Amine
 Sulfhydrl
OH
NH2
SH
WBL
92
Functional Groups
7/6/2015
WBL
93
Functions of Organic Matter
•
•
•
•
•
Source of nutrients for plant 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.
7/6/2015
WBL
94
Variable Charge on
Soil Organic Matter
COOH
OH - H+
O
COO+
OH - H
+ H+ O
+ H+ O
Acidic pH
7/6/2015
COOO-
Alkali pH
WBL
95
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.
7/6/2015
WBL
96
Complexation with Metals
COOH
OH
COO M
O
+ M2+
+ 2H+
O
O
Acidic pH
7/6/2015
Alkali pH
WBL
97
Greenhouse Gases
7/6/2015
WBL
98
7/6/2015
WBL
99
Methane Flux
(mg C-CO2/m2 day)
Methane Flux
400
300
200
100
0
0
2
4
6
8
10
12
Net Ecosystem Productivity (g C-CO2/m2 day)
7/6/2015
WBL
100
Methane Production
and Oxidation
O2
CH4
CH4
Water
O2 + CH4
CO2
CO2
Soil
7/6/2015
Organic
Matter
O2 + CH4
WBL
CH4
101
Carbon Cycle in Wetlands
UV
CO2
CO2 CH4
Decomposition/leaching
Decomposition/leaching
Litter
Import
Peat
Decomposition
leaching
Microbial
biomass
DOC
HCO3-
Microbial
biomass
DOC
HCO3CH4
Export
Decomposition/leaching
7/6/2015
WBL
102
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 complex 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

7/6/2015
WBL
103
Carbon Cycling Processes
Summary
Decomposition 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
(CO2. H2O, NO3-, SO42-, and Mn4+ and Fe3+ oxides), while the
anaerobic decomposition results in the production of reduced species
(H2, fatty acids, NH4+, N2, N2O, sulfides, CH4, Fe2+ and Mn2+)
 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

7/6/2015
WBL
104
Dissolved Organic Matter
7/6/2015
WBL
105
7/6/2015
http://wetlands.ifas.ufl.edu
http://soils.ifas.ufl.edu
WBL
106