Soil Mixing Effects on Inorganic Nitrogen Production and Consumption in Forest and Shrubland Soils

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Plant & Soil



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Soils that are physically disturbed are often reported to show net nitrification and NO3 loss. To investigate the response of soil N cycling rates to soil mixing, we assayed gross rates of mineralization, nitrification, NH+4 consumption, and NO3 consumption in a suite of soils from eleven woody plant communities in Oregon, New Mexico, and Utah. Results suggest that the common response of net NO3 flux from disturbed soils is not a straightforward response of increased gross nitrification, but instead may be due to the balance of several factors. While mineralization and NH+4 assimilation were higher in mixed than intact cores, NO3 consumption declined. Mean net nitrification was 0.12 mg N kg−1 d−1 in disturbed cores, which was significantly higher than in intact cores (−0.19 mg N kg−1 d−1). However, higher net nitrification rates in disturbed soils were due to the suppression of NO3 consumption, rather than an increase in nitrification. Our results suggest that at least in the short term, disturbance may significantly increase NO3 flux at the ecosystem level, and that N cycling rates measured in core studies employing mixed soils may not be representative of rates in undisturbed soils.

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