Nitrogen Dynamics of 15N-Labeled
Decomposing Fine Roots in
Western Oregon Forests
Tiffany van Huysen, Dr. Mark Harmon, and Dr. Steve Perakis
Department of Forest Science
March 5, 2004
Outline of Presentation





Introduction
Research Questions
Research Design and Methods
Impacts of 15N
Summary
Nitrogen Release from Litter
100
Fine Roots
Aboveground
Litter
% Ash-free Mass
Remaining
10
1
2
% Nitrogen
3
Research Questions
1. How does the relationship between mass loss
and N dynamics differ between aboveground
litter and fine roots?
2. What is the fate of 15N released from
decomposing litter?
Methods
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Field decomposition time series study
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Fate of 15N analysis study
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2 ½ years
2 years
Both studies will be conducted at
Cascade Head and H.J. Andrews
Experimental Forests
H.J. Andrews Plots
200-year Log Decomposition Experiment sites
physically adjacent to the placement of the ongoing Root
Decomposition Experiment of Chen Hua and the Fine Wood
Decomposition Experiment of Mark Harmon
Site 1
Site 2
Site 3
Field Decomposition Time Series Study

Litterbag technique
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1080 litterbags total
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Mesh, cloth/mesh, cloth
5 grams air-dried litter
540 bags per site
Subsamples of litter retained for initial
chemical analysis and moisture content
Experimental Design for Time Series Study
Western Oregon
Cascade Head
H.J. Andrews
Plot 1
Plot 2
Plot 3
Plot 1
Plot 2
Plot 3
Rep 1
Rep 1
Rep 1
Rep 1
Rep 1
Rep 1
Rep 2
Rep 2
Rep 2
Rep 2
Rep 2
Rep 2
Layout for Litterbags, 1 Replicate
1
2
3
4
5
6
10 m
10 m
= mesh or cloth/mesh
= cloth
7
Up Close with a Litterbag Line
1 meter
R
T
Douglas-fir
R = roots
N
R
T
N
Sitka spruce
T = twigs
N = needles
R
T
L
bigleaf maple
L = leaves
Fate of 15N Study
Randomized Complete Block design with 3 treatments and a control
C
R
T
N/L
R
R
R
R
R
R
R
R
R
C = control
R = roots
T= twigs
N/L= needles/leaves
Each circle = 1 planted seedling
Potential Impact of Adding 15N-Enriched Plant
Material to the Sites
Background = 0.3663 atom% 15N
Ecosystem N stock = 4930 kg N ha-1 (Sollins et al. 1980)
Plant N stock = 493 kg N ha-1
Addition rate = 0.45 kg N ha-1
Nitrogen Sink
Plants receive 15% of N addition
Enrichment
5%
99%
Plants
0.3705
0.4562
Ecosystem
0.3667
0.3753
Dilution of Tracer
Background = 0.3663 atom% 15N
Enrichment = 99%
0.3667
0.3691
0.3705
0.3691
0.3667
0.3691
0.3775
0.3775
0.3775
0.3691
0.3705
0.3775
0.4562
0.3775
0.3705
0.3691
0.3775
0.3775
0.3775
0.3691
0.3667
0.3691
0.3705
0.3691
0.3667
Dilution of Tracer
Background = 0.3663 atom% 15N
Enrichment = 5%
0.3663
0.3664
0.3665
0.3664
0.3663
0.3664
0.3668
0.3668
0.3668
0.3664
0.3665
0.3668
0.3705
0.3668
0.3665
0.3664
0.3668
0.3668
0.3668
0.3664
0.3663
0.3664
0.3665
0.3664
0.3663
Summary
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Nitrogen dynamics of fine root decomposition
with aboveground litter as a comparison
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Fate of 15N released from decomposing litter
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Field decomposition time series study
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Fate of 15N analysis study
Questions?