The effects of nitrogen deposition on carbon
sequestration in temperate forest soils
Preliminary results from studies of C in short N gradients (edges)
Shimon Ginzburg
1
Content
•Uncertainties in N deposition effects on the C cycle
•SOC accumulation in N deposition gradients in forest edges
•Objectives of study
•Methods: Sites, experimental set-up etc.
•Results
•Discussion? Conclusions?
•Temperature effects on SOM decomposition in C/N gradients
•Objectives
•Methods
•Results????
2
N deposition effects on the C cycle
Estimations of above-ground C accumulation:
15-40 kg C per kg N added (de Vries et al., 2009)
Uncertainty increase when we include soils:
5-225 kg C per kg N added
(de Vries et al., 2008;Magnani et al., 2007
;Magnani et al., 2008)
But most estimates for soils:
5-35 kg C per kg N added (de Vries et al., 2009)
70 kg C per kg N added (Gundersen et al., 2006a)
100 kg C ha-1 year-1 (Gundersen et al., 2006a).
Source: Gundersen et al. 2006
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Objectives of study
Overall objective: Quantify the effect of N deposition on C sequestration in temperate forest soils
More specifically:
Identify N deposition gradients in edge-interior transects in temperate conifer forests
Quantify the effect the excess N deposition has on the C stock in the top soil.
Hypothesis 1: Intermediate, long-term N deposition retards the decomposition of
SOM and leads to C accumulation in the forest soils.
Hypothesis 2: Under N saturated conditions the soil loses its capacity to sequester C.
•Focus is on the litter-fermentation-humus layer (LFH) and 0-5 cm soil layer
•We define intermediate deposition as 30-40 kg N ha-1 year-1 compared with high
deposition > 40 kg N ha-1 year-1
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Study site: Conifer
forests in Belgium and Denmark
Tree species
Belgium: Austrian pine (P. nigra)
Sønder Omme: Sitka spruce (Picea sitchensis)
Klosterhede: Norway spruce (Picea abies)
Thyregod: Norway spruce (Picea abies)
5
Experimental set-up and analysis
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Forest edge in Sønder Omme
7
Transect in Sønder Omme
8
Sampling of throughfall in Klosterhede
9
Sampling of organic and mineral soil
10
Results (1): N deposition gradient
N in throughfall
(kg N/ha/year)
Vloethemveld
70
60
50
40
30
20
10
Pinus nigra
P l (Pi
r = -0.783
p<0.05
0
20
40
60
80
100
i
)
120
Distance from edge (m)
Vloethemveld: Data from Wuyts et al. 2008
70
60
Thyregod
N in throughfall
(kg N/ha/year)
N in throughfall
(kg N/ha/year)
Klosterhede
Norway spruce and Silver fir
50
r = -0.901
p<0.05
40
30
20
10
0
20
40
60
80
100
120
70
60
50
40
30
20
10
Norway spruce
P l (N
)
r = -0.760
p<0.1
0
20
Distance from edge (m)
40
60
80
100
120
Distance from edge (m)
11
Klosterhede: data based on measurements during 3 summer months
Results (2): Soil C/N ratio
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Results (3): C content
So far – little evidence to support hypothesis 1: intermediate, long-term N deposition
retards the decomposition of SOM and leads to C accumulation in the forest soils.
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Results (4): N content
Sønder Omme
2.1
0.7
1.9
0.6
1.7
N content (t N/ha)
N content (t N/ha)
Vloethemveld
0.8
0.5
0.4
0.3
0.2
1.5
r=-0.839
p < 0.001
1.3
1.1
0.9
0.7
0.1
0.5
0
20
40
60
80
0
20
Distance from edge (m)
40
60
80
100
120
Distance from edge (m)
N content LFH fine
Thyregod
1.6
1.4
1.4
1.2
1.2
1.0
N content (t N/ha)
N content (t N/ha)
Klosterhede
1.0
0.8
0.6
0.4
N content mineral soil fine
0.8
0.6
0.4
0.2
0
20
40
60
80
Distance from edge (m)
100
120
0
20
40
60
Distance from edge (m)
80
100
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Results (5): C accumulation and C/N ratio
Stronger evidence to support hypothesis 2: Under N saturated conditions the soil loses
its capacity to sequester C.
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Discussion:
C/N ratio and C content
better correlation was found between the C/N ratio of the soil and its C content
Supports the second hypothesis: under N saturated conditions the soil loses its
capacity to sequester C, perhaps due to:
•reduced input of C originating from fine root growth (Persson et al. 1998)
•reduced input of C originating from soil bacterial biomass (Liu and Greaver, 2010)
Sønder Omme?
Vloethemveld?
Thyregod?
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What do we do now?
Isolate the effect of N on soil processes from other factors:
•Identify trends in root growth
•Estimation of litterfall input along the transects
•Measurements of light and temperature along the transects
•Work on more edge sites (Ulfborg, Denmark)
• N deposition and microbial populations (MSc. Thesis Ludovica Dímperio)
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Fine root growth as a function of distance from
the forest edge in Sønder Omme
Roots (g DW/ soil g FW)
0.025
0.02
r = 0.80
p < 0.001
0.015
roots MS
roots LFH
Linear (roots LFH)
0.01
0.005
0
0
20
40
60
80
100
120
Distance from edge
Sønder Omme
60
Fine roots: < 2 mm in diameter
High C close to edge in LFH layer – not
because of roots!
Organic C content (t C/ha)
50
40
r=-0.749
30
r=-0.227
20
10
0
0
20
40
60
80
Distance from edge (m)
100
120
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Litterfall measurements
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Annual litterfall input as a function of distance from the forest edge
In Klosterhede
Litterfall (g dry weight/ha/year)
250.00
200.00
150.00
TR A
TR B
100.00
50.00
0.00
0
20
40
60
80
100
120
Distance from edge (m)
Data based on 5 months measurements in 2 transects
No trend so far
No results yet for Sønder Omme
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Mean annual temperature and light intensity as a function of
distance from forest edge in Klosterhede
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Temperature:
2 replicates per distance
measured in one transect
Mean annual temperature (C)
3.8
3.6
3.4
r = - 0.695
p < 0.05
3.2
3
Small but significant difference
2.8
2.6
2.4
2.2
2
0
10
20
30
40
50
60
70
80
90
100
Distance from edge (m)
1200
Light intensity (LUX)
1000
Light:
No gradient
800
600
400
200
0
0
10
20
30
40
50
60
Distance from edge (m)
70
80
90
100
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Soil respiration in LF layer (mg CO2/ g C DW/hour) along
transects A and B in Klosterhede
Source: MSc. thesis Ludovica Dimperio (2011)
70.00
60.00
Water content (%)
50.00
40.00
LFH Fine
MS Fine
Poly. (MS Fine)
30.00
r = -0.036
p < 0.025
20.00
10.00
0.00
0
20
40
60
Distance from edge (m)
80
100
120
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Conclusions??????????
•Little evidence to support the assumption that high N deposition leads to
increased soil C content (Sønder Omme forest edge)
•Stronger evidence to support the assumption that under N saturated
conditions the soil loses its capacity to sequester C (Vloethemveld, Thyregod)
•C/N ratio can be related to C content in sites suffering from high long-term N pollution
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Temperature effects on SOM decomposition in
C/N gradients
Hypothesis: Effects of enhanced N deposition on decomposition of SOM can limit
temperature effects on SOM in forest soils
Klosterhede
Samples taken from edge and
N-addition experiment
40
C/N ratio
35
r=0.762
r=0.889
p< 0.0001
30
25
20
0
20
40
60
80
100
120
Distance from edge (m)
We will use the Q10 expression to show that decomposition rate of SOM
is expected to increase with temperature. However, we also expect lower Q10
values for soils characterised by low C/N ratio compared with those of high
C/N ratio (control)
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Basal respiration measurements
Incubation in a respirometer: 10 days under each of the following temperatures
regimes: 5,10,15,20,25ºC
In practice: 8,24,15ºC
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Results
Temperature effects on respiration of humus
0.035
0.03
H 8 degrees high N
0.025
H 15 degrees high N
0.02
H 24 degrees high N
H 8 degrees low N
0.015
H 15 degrees low N
0.01
H 24 degrees low N
0.005
0
0
5
10
15
Help!
20
-0.005
Temperature
25
30
Temperature effects on respiration of the LF layer
0.06
respiration (mg CO2/g dry soil/hour)
respiration (mg CO2/g dry soil/hour)
0.04
0.05
0.04
LF 8 degrees high N
LF 15 degrees high N
LF 24 degrees high N
0.03
LF 8 degrees low N
LF 24 degrees low N
0.02
0.01
0
0
5
10
15
Temperature
20
25
30
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One important thing to take home!
My e-mail: [email protected]
Or call me: +45-60889061
Thank you
Questions?
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