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, NH4+ 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 NH4+ 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.
Keywords: Disturbance N-15 isotope pool dilution - N mineralization - Nitrification - Microbial respiration