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INTERNAL NITROGEN CYCLING IN WESTERN OREGON FORESTS WITH DIFFERENT NITROGEN STATUS
Citation:
Shipley, E., C. Darr, AND J E. Compton. INTERNAL NITROGEN CYCLING IN WESTERN OREGON FORESTS WITH DIFFERENT NITROGEN STATUS. Presented at 4th North American Forest Ecology Workshop, Corvallis, OR, June 16-20, 2003.
Description:
Nitrogen incorporation and retention in forest ecosystems should vary with site N status, because nitrogen often limits temperate forest productivity and microbial activity. We followed the incorporation of a pulse of 15N-ammonium into the roots, microbes and soil organic matter of four forests across western Oregon, USA. The forests have a wide range of soil N content and mineral soil C:N ratios (<20-35). Two sites are located in the western Coast Range at low elevation (140 m) within 10 km of the ocean (Douglas-fir stand, and mixed red alder-conifer stand). The two other sites are located in the western Cascades, in Douglas-fir stands at low and high elevation (600 vs.1220 m). Watershed level N losses are generally higher in the Coast Range sites than in the Cascades. Preliminary data analysis indicates that incorporation of 15N into the O horizon is lower in Coast Range than Cascades forests, and lowest in the mixed alder-conifer stand with the highest N status. Over time, the O horizon released a higher proportion of the incorporated 15N in N-rich sites, while no 15N was released from the forest floor in the low N status site. Our work suggests that the internal cycling of N within the forest floor may play an important role in N dynamics at the ecosystem-to-watershed scale.