1. OUTLINE Why deal with decomposition Controls on decomposition
Intrinsic (biochemical composition)
Extrinsic (environment, nutrients, consumers)
Link from carbon to other elements
Discussion stream N export
What is not here
Detrital food webs
Dissolved Organic Carbon (DOC)

2. Decomposition - Closing the cycle Applies to all biologically relevant elements
CH2O
production
inorganic
organic
decomposition
CH2O
CO2 e-
ecosystem boundary
Fig. x. Weathers et al., Fundamentals of Ecosystem Science

3. Detritus Decomposition (Particulate Organic Matter)
Fig. 2 : Pathways of POM decomposition and interactions with other elements (nutrients)
Detritus Decomposition (Particulate Organic Matter)
DEAD PLANTS
Carbohydrates
Cellulose
Lignin
Protein
Lipids
DOC
Fungi
CO2
CH4
Bacteria
Fine
POM
N,P etc
External
Nutrients

4. Exponential Mass Loss dA/dt = kA A(t) = A(0)e-kt
EXAMPLES
k = 0.1/year
k=1/year
k=10/year
Half-Lives (yr)??
Leaching
Bulk POM decay
Amount
Recalcitrant
Time

5. CONTROL ON MASS LOSS - INTRINSIC
Structural complex molecules
Cellulose
Lignin
etc β β
CH2OH O OH OH
Cellulose
CH2OH OH O α OH
etc α
Both macromolecules are “sugar” C6H12O6
Bioavailability differs dramatically
Starch

6. Structural complex molecules
Cellulose
Lignin R OH
Hard to get at sub-units AND they are
not that useful once you get them.

8. EXTRINSIC (Environmental) CONTROL
Temperature
Nutrients
Organisms
(Arrhenius)
K=αe(-Ea/RT)
Increasing temp has positive effect on rate
increasing Ea has negative effect
Q10 ~ 2 near environmental conditions Ea
ENERGY
Strongly subject to environmental control
(Davidson and Janssens, Nature 2006;
Dorrepaal et al Nature 2009)
TIME

9. Exogenous Nitrogen Effect
See also Benstead et al 2009 Ecology

10. Control by terminal electron acceptor
CH2O + O CO2 + H2O Yield = 688kcal/mole
Aerobic Respiration
CH2O + NO CO2 + N2 Yield = 649
Denitrification
CH3COOH CH4 + CO2 Yield = 31
Methanogenesis

11. Responsible for bulk of mass loss
Microbes
Responsible for bulk of mass loss
Microbes
High biomass
Enzymatic capability

12. BUG EFFECTS Via Consumption of Detritus (see Swan & Palmer 2006)
Via Fragmentation

13. Effect of Macroinvertebrates

14. Animal Species Effects

15. BACTERIAL SPP RICHNESS (log scale 1-50 spp) RESPIRATION
Bell et al 2005 Nature 436:1157

16. Diversity Effects Meta-Analysis
Srivastava et al 2009 Ecology
Larger Top Down than Bottom Up effects
BU Effects exist but + and – cancel
Depends on choice of response variable

17. Connection to other Element Cycles
DEAD PLANTS
DOC
Fungi
CO2
CH4
Bacteria
Fine
POM
N,P etc
External
Nutrients

18. MASS LOSS TIME TO ½ MASS Fast – submersed (days-weeks) % ORIGINAL MASS
Medium – emergent
(months – year)
Slow – wood
(year – decade)
100%
Immobilization
% ORIGINAL MASS
Mineralization
Microbial biomass
TIME

19. PRODUCTS SUBSTRATE MICROBE Residue C = 50, N=1 C/N = 50 C = 40 C/N = 5
New cells
Residue
C = 50, N=1
C/N = 50
C=5
N=1
C = 40
C/N = 5
5 CO2
Small microbial biomass (limited by N),
incomplete OM decomp and no N release
C=25
N=5
C=50, N=5
C/N = 10
C = 0
25 CO2
Higher microbial biomass,
complete OM decomp and no N release
C=25
N=5
C=50, N=25
C/N = 2
N=20
25 CO2
High microbial biomass,
complete OM decomp and N is released

20. Decomposition - Closing the cycle Applies to all biologically relevant elements
CH2O
production
inorganic
organic
decomposition
CH2O
CO2 e-
ecosystem boundary
Fig. x. Weathers et al., Fundamentals of Ecosystem Science