Tuesday, 8 November 2005
9

Dissolved Organic Carbon and Nitrogen Ratios of Ponderosa Pine Forest Soils from Fire-Excluded and Frequently Burned Sites.

Rachel Brimmer and Thomas Deluca. Department of Ecosystem and Conservation Sciences, The University of Montana, Missoula, MT 59812

Nitrogen turnover tends to decline with increasing time since fire in ponderosa pine Pinus ponderosa and Douglas-fir Pseudotsuga menziesii forests of the Inland Northwest. This decline in N turnover may be due to an absence of recent charcoal deposition. Charcoal may alter N turnover by modifying carbon to nitrogen ratios in the soil solution or by the elimination of secondary plant metabolites that are otherwise inhibitory to soil microbes. Soil microcosms were leached successively with 5 pore volumes of water and extracts were analyzed for dissolved organic C, dissolved organic N and phenolic compounds. Potentially mineralizable N was measured by two week anaerobic incubation on soil from the same sites. Soils exposed to recent fire (charcoal present) appeared to adsorb a greater proportion of DOC than soils not exposed to fire. Results from these studies have the potential to enhance understanding of N cycling dynamics in both frequently burned and fire-excluded forest soils.

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