Graduate Thesis Or Dissertation
 

Modeling nitrogen fixation in dead wood

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nc580p91m

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  • A mechanistic simulation model of nitrogen fixation in dead wood was developed to help synthesize knowledge, develop hypotheses, and estimate rates of nitrogen fixation in the Pacific Northwest. In this model nitrogen fixation is directly controlled by log substrate, temperature, moisture, and oxygen content. Respiration and diffusion of oxygen indirectly affect nitrogen fixation and respiration by regulating log oxygen content. The relationships of abiotic and biotic variables on nitrogen fixation and respiration and the relationships of wood moisture and density were determined in laboratory experiments to parameterize the model. Nitrogen fixation and respiration had similar responses to temperature, with nitrogen fixation being optimum near 30°C and respiration being optimum over a broader range from 30°C to 50°C. Nitrogen fixation and respiration responded similarly to wood moisture with little activity below 50%, and optimal activity above 175% to 100% moisture content for nitrogen fixation and respiration, respectively. Nitrogen fixation was optimized at 2% 02. In contrast, respiration rates were optimal when 02 exceeded 1%. Nitrogen fixation and respiration in woody debris were significantly influenced by the degree of decay of the wood, and the woody tissue type, but not by the species of dead wood. In both the radial and longitudinal directions, the oxygen diffusion coefficient (Do2) in wood increased exponentially as the fraction of pore space in air (FPSA) increased and as density decreased. D02 in the longitudinal direction was 1.4 to 34 times greater than for the radial direction at zero and one FPSA, respectively. In comparison to independent data, the model of nitrogen fixation reasonably estimated seasonal patterns of log temperature, moisture, oxygen content, and respiration rate. The model estimates an annual nitrogen fixation rate of 0.7 kg N-ha-1 yr-1 for an oldgrowth stand at the H. J. Andrews, which is reasonably close to an independent estimate of 1.0 kg N-ha-1 yr-1 made for the same stand. Despite low annual rates of asymbiotic nitrogen fixation in wood, soil, and litter, this process can contribute 9% to 42% of a stands nitrogen inputs over succession when symbiotic fixers such as Alnus rubra and Lobaria oregana are present and absent, respectively. Managed stands with reduced levels of woody debris and litter may therefore be losing a significant nitrogen input.
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  • PDF derivative scanned at 300 ppi (256 B&W, 256 Grayscale), using Capture Perfect 3.0, on a Canon DR-9080C. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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