Litter mass declines exponentially with time

1
(No Transcript)
2
Litter mass declines exponentially with time
Mt M0 e-kt
At steady state, K calculated from both
approaches should be equivalent
Turnover time (TT) 1/k
3
Plant Litter Decomposition

• Microbial activity controlled by
• Environment soil T, H2O, soil O2
• Substrate chemical makeup of organic matter

Rate of microbial activity determines rate of C
loss, nutrient release etc.
Rate of activity measured as organic matter mass
loss decomposition
4
Substrate quality depends on
1. Size of molecule
2. Types of chemical bonds. sugars,proteins,organ
ic acids gt cellulose, hemicellulose gtlignin,
tannins
3. Regularity of structure
4. Toxicity
CN ratio?
5. Nutrient concentrations
5
Substrate quality differs by tissue/organ
6
Substrate quality differs by growthform
7
Substrate quality differs by environment
Lignin and rainfall are positively correlated
Lignin and decomposition rate are negatively
correlated
8
Ecosystem Decomposition
Environment Substrate Quality Species
Composition Allocation (stems, leaves, wood)
9
Ecosystem Decomposition
10
Ecosystem Carbon Balance
NEP GPP - Recosystem
Recosystem Rplant Rheterotrophs
Recosystem (50)Rplant (50)Rhet.
Rheterotrophs Rmicrobes Ranimals
Rheterotrophs (90)Rmicrobes (10)Ranimals
Is it all litter decomposition?
11
(No Transcript)
12

• Go to board

13
Soil Organic Matter
1. Partly decomposed (unrecognizable) plant
residues
2. Bodies of microorganisms involved in
decomposition
3. Byproducts of decomposition
14
Soil Organic Matter
CN Ratio SOM 10-121 Plant
Litter 20-4001 Bacteria 41 Fungi 101
SOM is 55 C 5 N 0.5 P 0.5 S
Alive Microbial Biomass (fungi, bacteria) 2-5 of
SOM Dead Non-humic substances 20-30 of
SOM Humic substances 60-80 of SOM
15
Humus (Latin for soil)
A continuum of organic matter decomposition from
fresh litter to well decomposed humus
Separation Schemes for operational
definition Chemical Separation Fulvic acids-
soluble in acid, base Humic acids- soluble in
base, not acid Humins - not soluble in base or
acid Density Separation Light SOM ( lt2.0
g/cc) Heavy SOM ( gt2.0 g/cc)
16
Humification
1. Selective preservation -- plant waxes, cutins,
suberin, lignin, chitin, microbial cell walls are
hard to decompose become enriched in soil
2. Microbial transformations -- enzymatic
breakdown by microbes produces low molecular
weight soluble compounds such as amino acids.
3. Polyphenol formation --phenols in soil are
derived from lignin breakdown, soil microbial
synthesis, and by plants as defensive compounds
17
Humification
4. Quinone formation -- conversion of polyphenols
to reactive quinones as a result of extracellular
enzymes
5. Abiotic condensation -- quinones react
spontaneously with many soil compounds such as
amino acids to form humus
18
Humus
Stabilized by interaction with soil mineral
surfaces
19
What controls the rate of soil organic matter
decomposition?
Think RH

• Usual suspects
• Moisture
• Temperature
• Nutrients
• O2
• Mechanical mixing/plowing
• Plant species change
• C additions priming the pumpthe Clarholm
  hypothesis
• Soil pedology parent material, weathering status
  

20
Soil Organic Matter
Active Soil C TT1.5 yr
Slow Soil C TT25 yr
Passive Soil C TT1000 yr
The century model
21
What controls the accumulation of soil carbon?
Carbon storage (kg m-2)
MAT (C)
MAP ( mm/yr)