Physiological response of Sphagnum
capillifolium and its N2-fixing community to
long-term addition of reduced and oxidised
nitrogen
Eva van den Elzen, Leon van den Berg, Bas van der Weijden,
Martine Kox, Katharina Ettwig, Leon Lamers, Lucy Sheppard
Peatlands: most important terrestrial soil carbon sink
From Heimann & Reichstein 2008
N cycle in bogs
upcoming
research
NP
P
Control
N
Anammox
From Rydin (2006)
The Whim Bog experiment
12 years of N addition
treatments:
- forms: NO3-, NH4+ or NH3
- loads: 16, 32, 64 kg/ha/yr
- Control: 8 kg/ha/yr
Species cover in Whim bog
Calluna vulgaris-Eriophorum vaginatum blanket mire:
Ericaceae (≈50%), graminoids (≈40%), Sphagnum spp (≈30%), other mosses (≈20%)
Sphagnum spp cover in 2011
Percentage cover Sphagnum spp (%)
45
40
35
30
25
20
15
10
5
0
control
16
32
64
control
NH₄
16
32
NO₃
Addition of N form and load
64
Research questions
- What is the effect of N addition in
different loads and forms on the amino
acid content of Sphagnum capillifolium?
-> increase N rich AA with increasing N load
- How do different forms of N addition
affect N2-fixation of microbes in
Sphagnum spp?
-> N2 fixation decreases with increasing N load
Sphagnum as a nitrogen filter
N2 fixation
N2 fixation?
N-rich amino acid
accumulation
Lamers et al.
2000
Nitrogen content of Sphagnum capillifolium
*
*
*
**
ha
Effect of 12 years of N addition on N rich amino
acids of Sphagnum capillifolium
Amino acid content of Glutamine
40
35
30
25
20
15
10
5
0
8
16
control
32
64
16
NH₄
32
64
NO₃
8
32
dry
contol
NH3
Amino acid content of Asparagine
µmol/g DW
14
12
10
8
6
4
2
0
µmol/g DW
µmol/g DW
Amino acid content of Arginine
45
40
35
30
25
20
15
10
5
0
8
control
16
32
NH₄
64
16
32
NO₃
64
8
32
dry
contol
NH3
8
control
16
32
64
NH₄
16
32
64
NO₃
8
32
dry
NH3
contol
treatment
N as % of total N
wet control
NH₄
NO₃
5.2
13.1
6.5
dry control
NH₃
11.3
18.1
Role N2 fixing microbes?
Sphagnum spp
Nitrogenase enzym:
8 H+ + 8 e- + N2
 2 NH3 + H2
16-24 ATP
 16-24 ADP + 16-24 Pi
Photo by Jacqueline Popma
Diazotrophic community of Sphagnum spp
NifH gene diversity
S. magellanicum
S. fallax
From: Bragina et al (2012)
N2 fixation experiment
Compare N2 fixation of microbe community of
Sphagnum spp in Whim bog with treatments of
different N forms:
32 kg/ha/yr NO3-, NH4+ and NH3
incubation of mosses with 10% 15N2
N2 fixation in Sphagnum spp vegetation bog
N2 fixation (nmol N /g DW/d)
160
140
120
100
80
60
40
20
0
dry con
dry NH3
S. capillifolium
wet con
S. papillosum
wet NH4
wet NO3
S. fallax
No inhibition of N2 fixation from 8 to 32 kg of all forms of nitrogen
Total N available for S. capillifolium from N2 fixation
>10% of total
available N
Total nitrogen fixed per hectare of bog
1
N2 fixation (kg/he/yr)
0.9
<1% of total
available N
0.8
0.7
0.6
0.5
S. capillifolium
0.4
S. papillosum
0.3
0.2
0.1
0
control
NH4
Treatment plots
NO3
In short…
• Sphagnum capillifolium can
function as a biomonitor for
different forms of N pollution
• N2 fixation of S. capillifolium
relevant to ecosystem N
budget
• Sphagnum - N2 fixating
microbes: from mutualism to
commensalism?
• Which factors other than N
deposition regulate N2
fixation?