Date of Award

Winter 2010

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Scott V Ollinger

Abstract

Abiotic immobilization of nitrogen may help explain nitrogen retention in soils under chronic nitrogen addition. Methodological limitations have made differentiating between abiotic and biotic immobilization in live soils difficult. This study attempted to make this differentiation with isotopically labeled nitrate, 15N18O3- . My hypothesis was that during biological reduction and assimilation of 15N, 18O would be lost as labeled water, but some 18O would be retained in abiotic reactions with soil chemicals. Lab incubations of soils from a Pinus resinosa stand were treated with 0.140 mg 15N g-1 dry soil of K15N18O3, for 0.25, 1 and 4 hours. Mean mass retained was 2.465 mug 15N (+/-0.208 mug), and 7.875 mug 18O (+/-0.677 mug). The ratio 18O:15N was inconsistent with a hypothesized limit of 2:1 for abiotic immobilization of NO3-, suggesting either biotic assimilation of 18O or unreacted 15N18O3-. Further investigation of this method is required before drawing conclusions on abiotic immobilization.

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