Nitrogen Dynamics of 15 N-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 15 N  Summary

Nitrogen Release from Litter % Ash-free Mass Remaining % Nitrogen Fine Roots Aboveground 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 15 N released from decomposing litter?

Methods  Field decomposition time series study  2 ½ years  Fate of 15 N analysis study  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 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 HeadH.J. Andrews Plot 1Plot 2Plot 3Plot 1Plot 2Plot 3 Rep 1 Rep 2 Rep 1 Rep 2 Rep 1 Rep 2 Rep 1 Rep 2

Layout for Litterbags, 1 Replicate = mesh or cloth/mesh= cloth 10 m

Up Close with a Litterbag Line 1 meter Douglas-firSitka sprucebigleaf maple RRRTTTNNL R = rootsT = twigsN = needlesL = leaves

Fate of 15 N 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 RR R RR R R Each circle = 1 planted seedling

Potential Impact of Adding 15 N-Enriched Plant Material to the Sites Enrichment Nitrogen Sink 5%99% Plants Ecosystem Background = atom% 15 N 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 Background = atom% 15 NEnrichment = 99%

Dilution of Tracer Background = atom% 15 NEnrichment = 5%

Summary  Nitrogen dynamics of fine root decomposition with aboveground litter as a comparison  Fate of 15 N released from decomposing litter  Field decomposition time series study  Fate of 15 N analysis study

Questions?