impact of long-term n fertilisation on c stocks in trees and soils in northern europe riitta...
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Impact of long-term N fertilisation on C stocks
in trees and soils in northern Europe
Riitta Hyvönen, Tryggve Persson, Stefan Andersson, Bengt Olsson,
Göran Ågren & Sune Linder
Biogeochemistry (Online)
Objectives
• To determine the efficiency of added N on C storage in trees and soils in 15 long-term experiments in Sweden and Finland
• To use data on N-use efficiency to draw conclusions about the role of 100 years of N deposition on C stocks
Methods
• Long-term (14-30 yrs) experiments with repeated (3-30 times) addition of N and/or NPK in doses of 30-200 kg N ha-1 occasion-1.
• Tree biomass: Stem diam, no. of trees ha-1 and Marklund (1988) expansion factors, C=50% of dry wt
• Soil sampling: Organic layer + 0-10 cm min. soil on, at least, one occasion
Norrliden (P. sylvestris )
020406080
100120140160
1970 1980 1990 2000
Tre
e b
iom
as
s C
(M
g h
a -1
)
N1N2N2PK, N3N1PKN3PK, 0PK
Stråsan (P. abies )
020406080
100120140160
1965 1975 1985 1995 2005
Tre
e b
iom
ass
C (
Mg
ha
-1)
N3PKN2PK
N1PKN2N1N3
PK0
Tree biomass C (above and below ground) in control plots (0) and after annual additions of ammonium nitrate (N), potassium and phosphorus (PK) or NPK at different doses (N1=33, N2=67, N3=109 kg N ha-1 yr-
1) at two sites.
Norrliden (P. sylvestris)
0
5
10
15
20
25
30
0 500 1000 1500 2000 2500
Cum amount of N added (kg N ha-1)
Cum
. inc
reas
e in
C p
ool i
nex
cess
of N
-free
plo
ts (M
g ha
-1)
N1
N2
N3
Stråsan (P. abies )
0
20
40
60
80
100
0 1000 2000 3000 4000Cum amount of N added (kg N ha-1)
Cu
m. i
ncr
ease
in C
po
ol i
n
exce
ss o
f N
-fre
e p
lots
(M
g h
a-1
)
N1
N2
N3
N1PK
N2PK
N3PK
Cum. increase in tree biomass C in excess of control plots as a function of the cumulative amount of N added. N1=33, N2=67, N3=109 kg N ha-1 yr-1.
Conclusion: Low application doses of N more efficient to sequester C than high N doses. Example: 35, 17, 9 kg (C) kg-1 (N) for N1, N2 and N3, respectively, at Norrliden).
N fertilisation only
-10
0
10
20
30
40
50
60
20 25 30 35 40 45 50 55C/N ratio in humus layer (control plots)
N-u
se
eff
. (k
g C
se
q. k
g-1
N)
PAFinland
PASweden
PSSweden
NPK fertilisation
-10
0
10
20
30
40
50
60
20 25 30 35 40 45 50 55C/N ratio in humus layer (control plots)
N-u
se e
ff. (
kg C
seq
. kg
-1 N
)N-use efficiency for C sequestration in tree biomass as a function of C/N ratios in humus layers of control plots after addition of N (left) or NPK (right) fertiliser at P. abies (PA) and Pinus sylvestris (PS) sites.
Conclusion: Soil N status (C/N) seems to regulate N-use efficiency in trees, but low C/N ratio often reflects low availability of P and K as seen by NPK addition.
N-use eff. in soil (N)
0
5
10
15
20
25
20 25 30 35 40 45 50 55
C/N ratio in humus layer (control plots)
N-u
se
eff
. (k
g C
se
q. k
g -1
N) P. abies
P. sylvestris
N-use eff. in soil (NPK)
0
5
10
15
20
25
20 25 30 35 40 45 50 55
C/N ratio in humus layer (control plots)
N-u
se
eff
. (k
g C
se
q. k
g -
1 N) P. abies
P. sylvestris
N-use efficiency for C sequestration in soil (org. layer + 0-10 cm min. soil) as a function of C/N ratios in humus layers of control plots after addition of N or NPK fertilisers
Relationship between N-use efficiencies in trees and soils for P. abies and P. sylvestris sites with both tree and soil studies. Figures from both N and NPK fertilisation. Conclusion: (1) Higher SOC seq. in P abies than in P sylvestris soils. (2) High SOC seq. also when trees don´t sequester extra C indicates reduced decomposition.
0
5
10
15
20
25
-10 0 10 20 30 40 50 60
N-use eff., kg (C) kg-1 (N), trees
N-u
se e
ff.,
kg (
C)
kg -1
(N
), s
oil
P. abies
P. sylvestris
C pool (kg m-2)
0
2
4
6
8
10
0 N1
LFH0-10 cm
Resp rate (mg C g-1 C d-1)
0,0
0,2
0,4
0,6
0,8
1,0
0 N1
Field Rh (g C m-2 y-1)
0
100
200
300
400
500
0 N1
LFH0-10 cm
Mean (SE, n=4) C pools, C mineralisation rates (at 15°C) and calculated field Rh to a depth of 10 cm in the mineral soil at Stråsan in control (0) and N-fertilised (N1) treatments in 2004. N1 had received, on average, 33 kg N ha-1 y-1 during 39 yrs.
Cumulative N deposition during the 20th century
0
200
400
600
800
1000
1200
1400
S Sweden N Sweden
Estim. increase in C pools (kg C
m-2) due to N deposition
0
1
2
3
4
5
S Sweden N Sweden
Trees
Soil
Estimates of cumulative N deposition in S and N Sweden during 1900-2000 and resulting tree and soil C pools as calculated from the N-use efficiencies
0.00
2.00
4.00
6.00
8.00
10.00
12.00
South Central North
Kg
C m
-2
Forest floor
Total 50 cm
Mean SOC content (±95% c.i.) for forest floor and total soil at dry and mesic forest sites in southern (55-60 oN, n= 445), central (60 – 64 oN, n=448) and northern Sweden (64-68 oN, n=329). After Mats Olsson, pers. comm.
Conclusions
• N-use efficiencies for trees (P abies) varied (0-50 kg (C) kg-1 (N)) depending on C/N ratio and PK availability.
• N-use efficiencies for SOC was generally lower than for trees and averaged 13 kg (C) kg-1 (N)) for P abies and 7 for P sylvestris.
• 10 kg N ha-1 yr-1 higher N deposition in S than in N Sweden for a whole century should have resulted in 2.0±1.0 kg m-2 more tree C and 1.3±0.5 kg m-2 more SOC.
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