1. Title: Decomposer metabolism and litter
decomposition rate as a function of climate and
elemental stoichiometry in terrestrial and aquatic
ecosystems
Master’s Thesis Presentation:
ecosystems
Presented by:
Mohammad Hafez Ahmed
Supervisor: Dr. Stefano Manzoni
Examiner: Dr. Steve W. Lyon
Department of Physical Geography, Stockholm University
Date: 12 May, 2016

2. Organization of Thesis
Chapter 1:- Introduction
• Background information
• Study Aim
Chapter 2:- Materials and methods
• Data collection
• Carbon-use efficiency (CUE) and Decomposition rate• Carbon-use efficiency (CUE) and Decomposition rate
constant [k; /yr]
• Climate and litter chemistry effects on CUE and k
• Relationship between CUE and growth rate [r; /yr]
• ANOVA test (Statistical significance test)
Chapter 3:- Results
Chapter 4:- Discussions
Chapter 5:- Conclusions

3. Background information (continue).
Litter decomposition:
Important for carbon-nutrient cycling and plant
productivity (Hobbie et al. 2013).
Decomposition: Physical and chemical changes of
litters.litters.
Decomposer metabolism:
• All biochemical reactions (catabolism and anabolism)
involved to maintain cell growth of organisms.
• Carbon-use efficiency (CUE) is the ratio of
microbial growth over carbon uptake (Manzoni et al, 2012).
Decomposition rate constant [k; /yr]:
• Relative mass loss rate per unit of time

4. Background information (continue).
CC C
Litter Decomposer
Uptake Release
CO2
C
N P
C C
N P
C stabilization
Nutrients
Figure: Conceptual diagram of litter decomposition.

5. Study aim
Main objectives:
• To estimate the bacterial CUE and decomposition
k of various litter types across terrestrial and
aquatic ecosystems.aquatic ecosystems.
• Climate (e.g. Temperature and precipitation) and litter
chemistry impacts on CUE and k.
• Is there any relationship between CUE and microbial
growth rate?

6. Materials and methods
Data collection:
Data types:
• Litter decomposition data (C/Co, N/No, P/Po, initial C/N and
C/P ratio.
• Climate data (temperature and precipitation)• Climate data (temperature and precipitation)
Sources:
• 28 literature sources for terrestrial ecosystems and 20 literature
sources for aquatic ecosystems including CIDET and LIDET
datasets.
• Climate research unit (CRU) and global map

7. Materials and methods (continue)....
Figure: A qualitative diagram from which data are collected and then
applied to models to estimate k and CUE

8. Materials and methods (continue)....
Figure: Study locations (small squares) around the world

9. Materials and methods (continue)....
)1.......(]
)(
)(
1[
)(
)(
)( 1
10,0,
e
B
N
B
N
c
N
C
N
C
N
C
N
C
ccn 

Decomposer CUE :
Eq. (1)- Initial
fraction of N as a
function of initial
fraction of CNN
Rate constant k:
)3......()1(
)2.......(
21
0
tktk
ktt
eeC
e
C
C
C





•Note: Decomposer (C/N)B ratio : 5 to 15 (Manzoni et al. 2008)
[ Assumed , (C/N)B = 10]
[Single-pool model (mostly used)]
[Double-pool model]

10. Materials and methods (continue)....
)5.....(ln)
1
)(()ln(
)4.......(
A
TR
E
CUE
RT
E
AeCUE





Climate effect on CUE:
[Arrhenius function]
TR
Litter chemistry effect on CUE :
)7.......(ln)ln(*)ln(
)6........()(
ACNRbCUE
CNRACUE b

  [Power-law]

11. Materials and methods (continue)....
1
)8.......(
E
RT
E
Aek





Climate effect on k:
[Arrhenius function]
Temperature effect: Precipitation effect:
1. Exponential function
2. Power-law function
3. Linear fit
)9.....(ln)
1
)(()ln( A
TR
E
k 


Litter chemistry effect on k :
)11.......(ln)ln(*)ln(
)10........()(
ACNRbk
CNRAk b

 
[Power-law]

12. Materials and methods (continue)....
)13)....((*)(*
)12......(
11
L
CCUE
kr
G
Yr
m
CUE


Relation between CUE and growth rate [r; /yr]:
[Pirt (1965)]
)13)....((*)
1
(*
MB
C
L
C
CUE
CUE
kr


•CMB/CL varies 1-3% (van Meeteren et al. 2008), assumed= ~2%

13. Materials and methods (continue).
ANOVA test: statistical significance test

14. Results and discussions
N release pattern and decomposer CUE
Litter
type
Terrestrial
CUE
Aquatic
CUE
Grass 0.21 0.24
Broadleaf 0.26 0.19
Table: Average CUE
Figure : Nitrogen release pattern for a specific value of CUE.
Needle 0.17 0.15
Root 0.12 0.12
Wood 0.09 0.04

15. Results and discussions (continue)...
Figure: CUE-T relationship Figure: CUE- precipitation relationship
•Terrestrial ecosystems show a positive relationship with
temperature and precipitation, whereas aquatic ecosystems
demonstrate the opposite patterns.

16. Results and discussions (continue)...
Figure: One-way ANOVA (across temperature windows)
Figure: One-way ANOVA (across precipitation windows)

17. Results and discussions (continue)...
)6........()(
b
CNRACUE


Figure: ln(CUE) vs. ln(CN0) relationship
•Relationship is steeper in aquatic systems compared
to terrestrial systems.
)7.......(ln)ln(*)ln( ACNRbCUE 

18. Results and discussions (continue)...
Decomposition k
Figure: Changes in C mass in litter using decomposition models
)3......()1(
)2.......(
21
0
tktk
ktt
eeC
e
C
C
C






19. Results and discussions (continue)...
Table: Decomposition rate constants, k
Terrestrial ecosystems Aquatic ecosystems
Aquatic grass and broadleaf litter types have significantly
higher k values than terrestrial grass and broadleaf litter types.

20. Results and discussions (continue)...
Figure: ln(k) vs. 1/T graph
Table: Activation energy in ecosystems
)9.....(ln)
1
)(()ln(
)8.......(
A
TR
E
k
RT
E
Aek





•Have warmer climate and
lower value of CN0, but higher
E for aquatic grass and root
litter.
•Indicates a shift from the
Arrhenius-type assessment of
temperature sensitivity.
Table: Apparent E of litter types

21. Results and discussions (continue)...
Table: k vs. precipitation relationships
• k-value has a little sensitivity with precipitation.
•Only important in terrestrial ecosystems for
enzyme transportation.

22. Results and discussions (continue)...
Table: ln k vs. ln(CN0) relationship
)11.......(ln)ln(*)ln(
)10........()(
ACNRbk
b
CNRAk



•Relationship is more steeper
in aquatic ecosystems

23. Results and discussions (continue)...
Table: Summary of significant regression analyses
Terrestrial ecosystems
Aquatic ecosystems

24. Results and discussions (continue)...
Most influencing parameter in litter decomposition
•Temperature is the main
parameter in terrestrial ecosystems
across the biomes. •Litter chemistry is the mostacross the biomes.
•Within a biome litter chemistry is
dominant parameter, except in
tundra regions
•Litter chemistry is the most
important parameter in
aquatic ecosystems within a
biome and across the biomes
Terrestrial ecosystems Aquatic ecosystems

25. Results and discussions (continue).
CUE vs. Growth rate:
Figure: Double reciprocal graphs of microbial CUE and growth rate r
• Two parameters are positively
correlated in both ecosystems,
whereas questions arise in case
of aquatic grass and needle litter
types.
)13)....((*)
1
(*
)12......(
11
MB
C
L
C
CUE
CUE
kr
G
Yr
m
CUE




26. Conclusions
• Temperature and precipitation do not matter for CUE
in both ecosystems.
• CUE decreases with increased CN0 of litter in both
ecosystems.
• Temperature is the main predicting parameter of• Temperature is the main predicting parameter of
litter decomposition in terrestrial ecosystems at the
larger scale. In contrast, litter chemistry is of
primary importance in aquatic ecosystems.
• Microbial growth rate is positively correlated with
CUE

27. Thank you for listening !!!
Questions? Questions? 