Feedback of Below Feedback of Below Feedback of Below Ch M di t d b M Change Mediated by M Change Mediated by M g y
Christina Kaiser Christina Kaiser Oskar Franklin (Ecosys Oskar Franklin (Ecosys
A d Ri ht (D t t
Andreas Richter (Department ( p Ulf Dieckmann Ulf Dieckmann
B k d
Background Background
Mi bi l d d ti f l t litt d il i t i l (“ il i ti ”) Microbial degradation of plant litter and soil organic material (“soil respiration”) causes an annual CO2 flux equivalent to 8% of today’s atmospheric carbon
causes an annual CO2 flux equivalent to 8% of today s atmospheric carbon
l A h i thi t i ifi tl i fl th t h i
pool. Any changes in this rate may significantly influence the atmospheric carbon (C) budget Soil respiration has been found to be sensitive to
carbon (C) budget. Soil respiration has been found to be sensitive to
t t i t ll t C d t i t il biliti R t
temperature, moisture as well as to C and nutrient availabilities. Recent studies have shown that changes in soil respiration rates were most often studies have shown that changes in soil respiration rates were most often
i d b h i i bi l i i i i i
accompanied by changes in microbial community composition, pointing to a p y g y p p g link between community structure and function Despite its significance for the link between community structure and function. Despite its significance for the global C budget, the mechanisms underlying the degradation of soil organic
g g , y g g g
material are still only poorly understood material are still only poorly understood.
Modeling microbial functional groups Modeling microbial functional groups g g p
Spatially structured: 10 000 Functional traits e g :
• Spatially structured: 10.000 Functional traits, e.g.:
P d ti f ifi
microsites on a two-dimensional gridg • Production of specific enzymes
• Each microsite can be inhabited by y • C and N demand
one microbe belonging to a specific
C and N demand
one microbe belonging to a specific
f ti l One microsite CO2
functional group One microsite
F ti l h t i d Decay ofenzymes
• Functional groups are characterized Decay ofenzymes Enzymes by functional traits Oxidase Chitinase Protease
by functional traits
Complex
• Microbes carry out carbon and y substrate Enzymatic B l t nitrogen (N) transformations in each SOM
y
breakdown Belongs to a
microbial f ti l
nitrogen (N) transformations in each
i i
SOM functional group
microsite
Micro
Cell walls
Diff i f l bil b t
Micro- organism
Cell walls
• Diffusion of labile substances across
Proteins
Mineralisation and immobilisation
the grid enables competitive and
Proteins immobilisation
the grid enables competitive and synergistic interactions
synergistic interactions microbialdead DOM DIN
Mi bi l
• Microbial community dynamics
biomass Microbial
biomass recycling
Labile substrates
• Microbial community dynamics Labile substrates
emerge as a result and feed back on g degradation processes and thus
degradation processes and thus il bilit
Diffusion of labile
resource availability. substrates to and from
neighbouring cells
Rhizosphere priming Rhizosphere priming p p g
Labile C released by plant roots is known to enhance degradation of soil Labile C released by plant roots is known to enhance degradation of soil
i tt ll d “ hi h i i ” Th h i b hi d
organic matter, a process called “rhizosphere priming”. The mechanism behind it is still unclear although priming is increasingly considered as a major factor it is still unclear, although priming is increasingly considered as a major factor
i th t f il C t R t t di h h th t th
governing the rate of soil C turnover. Recent studies have shown that the
amount of C released by plant roots is increasing with increasing atmospheric amount of C released by plant roots is increasing with increasing atmospheric
CO t ti hi h ff t il C t l b l l
CO22 concentrations, which may affect soil C turnover on a global scale.y g
Concentration of Distribution of microbial groups along a growing root releasing labile carbon Concentration of
labile s bstances Distribution of microbial groups along a growing root releasing labile carbon
labile substances
Dissolved organic Dissolved organic matter
matter
high high
low
Ammonium
low
´ Opportunistic microbes SOM degrading specialists Generalists Ammonium and Nitrate
Our model results demonstrate that the local input of labile C along a growing Our model results demonstrate that the local input of labile C along a growing
t i di t l t t th hi h it F t i
root immediately structures the rhizosphere community. Fast growing,
opportunistic microbes (red) thrive directly at the roots surface Around them opportunistic microbes (red) thrive directly at the roots surface. Around them
d i ll t th i t ti l f il i tt d di
and especially at the growing root tip a layer of soil organic matter degrading microbes (blue) forms utilizing energy and nutrients being released from the microbes (blue) forms utilizing energy and nutrients being released from the
t d th t f t i ti i b Thi l d t hi h t f
root and the turnover of opportunistic microbes. This leads to higher rates of soil organic matter degradation around the growing root tip
soil organic matter degradation around the growing root tip.
wground Processes to Global wground Processes to Global wground Processes to Global
Mi bi l C it D i
Microbial Community Dynamics Microbial Community Dynamics y y
r (Evolution and Ecology Program IIASA) r (Evolution and Ecology Program, IIASA)
stem Services and Management Program IIASA) stem Services and Management Program, IIASA)
f T t i l E t R h U i it f Vi A t i )
of Terrestrial Ecosystem Research, University of Vienna, Austria) y , y , ) (Evolution and Ecology Program IIASA)
(Evolution and Ecology Program, IIASA)
A il l i l t
A soil ecological concept A soil ecological concept
S il i l d h t i t i ti f
• Soil is a complex and heterogeneous environment consisting of a g g
magnitude of microsites with different abiotic conditions and resource magnitude of microsites with different abiotic conditions and resource
il bili i hi h h i ll hi h bi di i f il
availabilities, which promotes the exceptionally high biodiversity of soil p p y g y microbes
microbes
• Different microbial species fulfill different functions in the soil and haveDifferent microbial species fulfill different functions in the soil and have
di ti t t i t d d d (f ti l di it )
distinct nutrient and energy demands (functional diversity).
Th d d ti f h i ll l i t i l i th
• The degradation of chemically complex organic material requires the concerted action of species with different functional traits
concerted action of species with different functional traits.
C b d
Carbon and
Understanding mechanisms of
Nitrogen availability g
soil carbon turnover requires soil carbon turnover requires understanding the link
Mi bi l it understanding the link
Microbial community
between resource availability,
composition y
microbial community microbial community
dynamics and soil processes
Soil organic matter
dynamics, and soil processes.
decompositionp
Litt d iti
Litter decomposition Litter decomposition
Pl t litt d iti i th l t t f th b (C) fl f
Plant litter decomposition comprises the largest part of the carbon(C) flux from terrestrial ecosystems to the atmosphere Litter decomposition rates have
terrestrial ecosystems to the atmosphere. Litter decomposition rates have
b f d t d d ( t th ) it (N) il bilit f
been found to depend (amongst others) on nitrogen (N) availability for p ( g ) g ( ) y
microbes Increasing N input into natural ecosystems from industrial sources microbes. Increasing N input into natural ecosystems from industrial sources gradually increase N content in plant litter, which may affect its decomposition
g y p , y p
rate Litter decomposition is usually accompanied by a succession of microbial rate. Litter decomposition is usually accompanied by a succession of microbial groups.
g p
Nitrogen-rich litter g Nitrogen-poor litter (C:N ratio 40)
Nitrogen poor litter (C:N ratio 60)
(C:N ratio 40) (C:N ratio 60)
opportunistic microbespp plant material degrading specialists
specialists
dead microbial biomass degrading specialists degrading specialists
Day 75 Day 550 Day 75 Day 550
Day 75 Day 550 Day 75 Day 550
1.2
on)
1.0
rbon carbo
0.8 N-poor litter (C:N 60)
ng car litter
0.6
mainin initial
0 4 N i h li (C N 40)
rem (g.g-1
0 2
0.4 N-rich litter (C:N 40)
( 0.2
0 200 400 600 800 1000 1200
0.0
time (days)
Distribution of microbial groups over Overall carbon loss from decomposition Distribution of microbial groups over time with initial litter C:N=40 in the two litter types. time with initial litter C:N=60
Our model shows strong interactions between the chemical transformation of Our model shows strong interactions between the chemical transformation of litter and microbial community dynamics during the decomposition process.
litter and microbial community dynamics during the decomposition process.
The initial C:N ratio determines the rate of decomposition by mediating a The initial C:N ratio determines the rate of decomposition by mediating a specific microbial community dynamics.
specific microbial community dynamics.
Model calibration
500
Model calibration CO2 respiration
day-1
400
Model output versus CO2emission
total C Model output versus
data for microbial
Model parameters were calibrated using a Bayesian
-C g-1 t 300
respiration during
approach (Markov-chain Monte Carlo): 15 model output
m CO2-
200 litter decomposition:
circles: empirical
pp ( ) p
variables were fitted to empirical measurements obtained crogram 100
circles: empirical measurements,
p
during a long time litter decomposition experiment. mi
c lines: model output
during a long time litter decomposition experiment.
0 100 200 300 400 500 600
0
days
Conclusion Conclusion
We integrated microbial ecology into a biogeochemical model in a bottom-up g gy g p approach Soil respiration rates emerge as a result of ecological interactions approach. Soil respiration rates emerge as a result of ecological interactions between microbes at the individual level. Model results are consistent with empirical observations and provide insights into the mechanisms driving soil empirical observations and provide insights into the mechanisms driving soil organic matter turnover. Our results demonstrate the importance of dynamic organic matter turnover. Our results demonstrate the importance of dynamic interactions between microbial communities and soil organic matter turnover at interactions between microbial communities and soil organic matter turnover at the microscale, which may drive the overall response of soil CO2 emissions to the microscale, which may drive the overall response of soil CO2 emissions to changing en ironmental conditions
changing environmental conditions.
