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

% Ash-free Mass

Remaining

% Nitrogen

1 2 3

100

10

Fine RootsAboveground Litter

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

Field decomposition time series study 2 ½ years

Fate of 15N analysis study 2 years

Both studies will be conducted at Cascade Head and H.J. Andrews Experimental Forests

H.J. Andrews Plots200-year Log Decomposition Experiment sitesphysically adjacent to the placement of the ongoing Root Decomposition Experiment of Chen Hua and the Fine Wood Decomposition Experiment of Mark Harmon

Site 3

Site 2

Site 1

Field Decomposition Time Series Study

Litterbag technique Mesh, cloth/mesh, cloth 5 grams air-dried litter

1080 litterbags total 540 bags per site

Subsamples of litter retained for initial chemical analysis and moisture content

501

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 2

Rep 1

Rep 2

Rep 1

Rep 2

Rep 1Rep 1

Rep 2 Rep 2Rep 2

Layout for Litterbags, 1 Replicate1 2 3 4 5 6 7

= mesh or cloth/mesh

= cloth

10 m

10 m

Up Close with a Litterbag Line

1 meter

Douglas-fir

Sitka spruce

bigleaf maple

R RR TT T NN L

R = roots

T = twigs

N = needles

L = leaves

Fate of 15N Study

C

T

R

N/L

C = control

R = roots

T= twigs

N/L= needles/leaves

Randomized Complete Block design with 3 treatments and a control

R

R

R R

R

R R

R

R

Each circle = 1 planted seedling

Potential Impact of Adding 15N-Enriched Plant Material to the Sites

Enrichment

Nit

rog

en

S

ink

5% 99%

Plants

Ecosystem

0.3705

0.3667

0.4562

0.3753

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

Plants receive 15% of N addition

Dilution of Tracer

0.4562

0.37750.37750.3775

0.37750.3775

0.37750.37750.3775

0.36670.36910.37050.36910.3667

0.36910.3691

0.37050.3705

0.36910.3691

0.36670.36910.37050.36910.3667

Background = 0.3663 atom% 15N Enrichment = 99%

Dilution of Tracer

0.3705

0.36680.36680.3668

0.36680.3668

0.36680.36680.3668

0.36630.36640.36650.36640.3663

0.36640.3664

0.36650.3665

0.36640.3664

0.36630.36640.36650.36640.3663

Background = 0.3663 atom% 15N Enrichment = 5%

Summary

Nitrogen dynamics of fine root decomposition with aboveground litter as a comparison

Fate of 15N released from decomposing litter

Field decomposition time series study

Fate of 15N analysis study

Questions?