Citation:

Holub*, S M., K. J. Lajtha, J. SPEARS, J. Toth, S. E. Crow, B. A. Caldwell, M. Papp, AND P. T. Nagy. NITROGEN DEPOSITION AND ORGANIC MATTER MANIPULATIONS AFFECT GROSS AND NET NITROGEN TRANSFORMATIONS IN TWO TEMPERATE FORESTS SOILS. doi:10.1016/j.foreco, P.M. Attiwill (ed.), FOREST ECOLOGY AND MANAGEMENT. Elsevier Science Ltd, New York, NY, 214(1-3):320/330, (2005).

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Soil nitrogen transformations are intricately linked to carbon transformations. We utilized two existing organic matter manipulation sites in western Oregon, USA and Hungary to investigate these linkages. Our questions were: 1) Does the quantity and quality of organic matter affect net and gross N processing in mineral soil? 2) Do these effects vary under high versus low atmospheric N deposition? The organic matter manipulations had a small if any effect on gross and net N cycling rates and N pool sizes. Gross N cycling rates under low N deposition increased with increasing soil C and N, but C:N ratio had no correlation with gross N cycling rates. Soil ammonium concentrations under high N deposition, however, were higher in the organic matter manipulation plots without roots and lower in plots with double litter, indicating a tree root effect and a litter immobilization effect, respectively, but did not differ significantly under low N deposition. Net ammonium production was lower in the litter removal and root removal plots and highest in the litter addition plots at both sites. Gross and net N cycling rates and mineral nitrogen pool sizes were generally higher under higher N deposition and lower C:N ratio soil, which was consistent with past studies over gradients of N deposition. By looking at organic matter manipulations under two very different N deposition scenarios we gained some insight into the role that C:N ratio as well as total C and total N have in controlling N and C cycling in forest soils.

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