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Publication Title:   Modeling asymbiotic nitrogen fixation in woody detritus as a nitrogen input in Pacific Northwest forests [Abstract]

Year:  1999     Publication Type:  Abstract

H. J. Andrews Publication Number:  293

Citation:  Hicks, W. T.; Harmon, M. E. 1999. Modeling asymbiotic nitrogen fixation in woody detritus as a nitrogen input in Pacific Northwest forests [Abstract]. In: The Ecological Society of America 84th annual meeting: legacies, landscapes and limits: bridging borders; 1999 August 8-12; Spokane, WA. Washington, DC: Ecological Society of America: 108.

Online PDF:  http://andrewsforest.oregonstate.edu/pubs/pdf/pub293.pdf

Abstract:  Asymbiotic nitrogen fixation is known to occur in woody debris; however,the importance of this process as a nitrogen input for forests is poorly under-stood. We constructed a mechanistic simulation model driven by tempera-ture, moisture, oxygen concentration. and substrate quality to estimate annualnitrogen fixation rates in logs over a year. Temperature and moisture are di-rect inputs, whereas respiration and oxygen diffusion determine oxygen con-centrations within logs. Acetylene reduction (AR) calibrated with '51‘12 wasused to construct response curves and indices for input variables. Log levelresponses were scaled up to the stand level using inventories of woody debrismass by species and decay class. Preliminary AR results show nitrogen fixa-tion rates are optimum at 30°C, 3% oxygen, and 100% or greater wood mois-tures. Nitrogen fixation rates appear to peak in moderately decayed woodwith little activity in late decay stages. Our model estimates a hypothetical1.5 Mg log decaying for 200 yr can fix 0.27 kg N. Model results demonstrateseasonal changes in nitrogen fixation rates spanning an order of magnitude.Preliminary stand level estimates of nitrogen fixed by woody debris of 1 kgN/ha/year agree with other studies. This modeling analysis illustrates sensi-tive areas and directs future research needs.

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Hicks ,  William   T.
Harmon ,  Mark   E.

Nitrogen cycling
Nitrogen fixation
Woody debris

Pacific Northwest