Partitioning root derived soil
respiration through δ13C
measurements in a long-term
field experiment in Ultuna,
Sweden
Lorenzo Menichetti*1, Alf Ekblad2, Thomas Kätterer1
1 = SLU (Swedish University of Agricoltural Sciences), 2= Örebro University
*any questions?
Lorenzo Menichetti
SLU, Mark Och Miljö department,
Uppsala (75007) /
[email protected]
2nd NordSIR meeting "Stable Isotope
studies on carbon and nitrogen cycling“,
Denmark, 3-5 October 2011
Intro
δ13C in microbial respiration
Utilizing a δ13C natural labeling we
calculated the contribution of recent
root-derived material to the soil
respiration, exploring different
possibilities to define the mixing
model and the pools involved
Roots
Microbes
SOM
2
The Experiment
The Ultuna C-SOME
The Ultuna Continuous Soil Organic Matter
Experiment (C-SOME) was initiated in 1956 to
test the effect of a wide range of fertilization
treatments in a cool temperate site (59° 48’,
17° 39’) in Ultuna, Sweden on an Haplic
Cambisol (eutric).
The site is hand ploughed every year, and fertilized
with different materials every 2 years.
Soil is taken every year and archived; every
two years C and N are analyzed.
3
The Experiment
The different treatments
C% (0-20 cm)
CarbontrendsintheUltunaC-SOME
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
without organic matter, without N, naked soil
without organic matter, without N, cultivated
without organic matter, 80 kg/ha N Calcium Nitrate
without organic matter, 80 kg/ha N Ammonium Sulphate
without organic matter, 80 kg/ha N Calcium Cyanamide
4 t / ha C in straw, every two years, without nitrogen
4 t / ha straw C, every two years+ 80 kg/ha N Calcium Nitrate
4 t / ha green C mass every two years, without N
4 tons / ha C peat every two years, without N
4 t / ha C green manure every two years, without N
4 t / ha C cattle manure every two years, without N
4 t / ha C sawdust every two years, without N
4 t / ha C peat every two years + 80 kg/ha N Calcium Nitrate
4 t / ha C sawdust every two years + 80 kg/ha N Calcium Nitrate
4 t / ha C sewage sludge every two years, without N
4
The Experiment
Chosen Treatments
In year 2000 the cultivation of the
experiment has been shifted from
C3 to C4 plants (maize)
We concentrated on 5 different treatments representative of the whole SOM range:
A
B
C
G
O
Fallow plot, kept unvegetated since the start of the experiment. In this
plot we assumed no inputs
Not fertilized plot. One C source composed by vegetal inputs (assumed to
be roots since the aerial part is removed)
Nitrogen fertilized plot. One C source composed by vegetal inputs
(assumed to be roots since the aerial part is removed)
Straw + Nitrogen amended plot. Two different C sources, roots and
amendmen
Sewage sludge + Nitrogen amended plot. Two different C sources,
roots and amendmen
}
}
2 sources mixing model
3 sources mixing model
5
Matherials & methods
Field and lab measurements
We analyzed the δ13C signature of
the soil together with plant and
amendment samples.
We then measured directly on the
field in May 2011 (bare soil) the
δ13C signature of the soil microbial
respiration with a Picarro cavity
ringdown spectrometer.
6
Matherials & methods
The Picarro G1101-i cavity ringdown spectrometer
Near-infrared laser spectrometer
(adapted for field soil measurements)
•
•
•
Cheap
Robust
Stable
•
•
Slow
Relatively low precision (sensitive
to field condition)
It’s based on the decay of a
laser photon beam in a mirror
ring. the effective path length
within the cavity can be over
20 kilometers
7
Matherials & methods
The Picarro G1101-i cavity ringdown spectrometer
Continuous airflow through the instrument
The plot (a moving regression resulting from the
mixing of atmospheric and soil CO2) needs time to
stabilize. With good readings at least 11 minutes are
needed with a flow of approx 24ml/min
Keeling 5 min
Keeling 10 min
0.00
0.00
10.00
20.00
30.00
0.00
10.00
20.00
30.00
-5.00
-10.00
-15.00
-20.00
-25.00
-30.00
-35.00
8
Results
Field measurements
}
}
No changes
Proportional
to inputs
Proportionality between
input quality (carbon
trend) and soil activity
Influence of
amendments
9
Some results
From previous studies
Proportionality
between input quality
(carbon trend) and soil
activity
(1)
(1, 2)
(1)
1= G. Börjesson, T. Kätterer , H. Kirchmann , L. Menichetti (in press), Soil microbial
community structure affected by 53 years of nitrogen fertilisation and different organic
amendments. Biology and Fertility of Soils, accepted on 9 September 2011
2= K. Enwall, K. Nyberg, S. Bertilsson, H. Cederlund, J. Stenström, S. Hallin (2007) Longterm impact of fertilization on activity and composition of bacterial communities and
metabolic guilds in agricultural soils. Soil Biology and Biochemostry 39:106-115
10
Calculations
proposed approach nr 1: pure sources mixing
Assumptions
•
There is no metabolic fractionation: the
δ13C of the respiration is the same of
the substrate
•
The mixing is between two pure
sources: no other proportionality
coefficient is involved
1
1
Results
Approach nr.1
Fallow
Cultivated
Cultivated + N
0%
33 %
39 %
61 %
100
%
Cult+N+Straw
30 %
Cult+N+Sludge
30 %
70 %
67 %
C3 SOM + amendments
70 %
C4 SOM + fresh C4 inputs
12
Calculations
proposed approach nr 2: SOM pools mixing
B and C plots
Not Amended
SOM contribution
We utilized a mass balance equation to
describe the mixing of two sources in the
not amended treatments, assuming SOM
and roots as the two sources of C for the
respiration, to determine the fraction (f)
expressing the contribution of roots to
the measured respiration
G and O plots
Roots contribution
SOM + amendment contribution
Amended
In the amended plots the equation has
been modified to account for the
amendments, still separating two pools
(SOM+amendment and roots)
We utilized a linear optimization procedure to calculate the source contribution proportion for every
treatment.
1
3
Calculations
approach nr. 2 assumptions
Assumptions
•
•
•
•
The fallow has zero input (so it has
been excluded from the coefficient
calculation)
There is no metabolic fractionation
The three pools are defined by their
ages, have homogeneous quality
The different pools are identified
through the C inputs and a
“humification coefficient”
(1-f)
(f)
>56 years
Old pool
2 years
2 years
Young pool
(amendments)
Young pool
(roots)
1
4
Results
Approach nr.2
Fallow
Cultivated
Cultivated + N
0%
20 %
34 %
80 %
100
%
66 %
Cult+N+Sludge
Cult+N+Straw
14 %
16 %
SOM (old pool) + amendments
84 %
86 %
SOM (young pool, 2 years old)
15
Future developments
Possible improvements
•
The same data and the conceptual model will be used to test the sensitivity of the results to the
hypothesis of a proper fractionation (metabolic or through differential substrate utilization)
operated by the microbes between inputs and respiration (in form of an additive factor to the δ13C
signature of the input material) .
•
An error propagation procedure will be implemented in this conceptual model utilizing a stochastic
framework (iterated simulations) for the paramenter calibration
•
The procedure will be extended to include the instant fluxes from the plants measured by difference
during the growing season. Measurements are being performed.
16
Future developments
Following steps
Possible different partitioning
strategies through
modelling:
Assumptions can be tightened
or relaxed to target
different pool.
17
THANK YOU
for your attention
*any questions?
Lorenzo Menichetti
SLU, Mark Och Miljö department,
Uppsala (75007) /
[email protected]