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This article in SSSAJ

  1. Vol. 71 No. 3, p. 836-842
    Received: Sept 27, 2006

    * Corresponding author(s): georgev@csusm.edu


Chronic Nitrogen Deposition Enhances Nitrogen Mineralization Potential of Semiarid Shrubland Soils

  1. George L. Vourlitis *,
  2. Gypsi Zorba,
  3. Sarah C. Pasquini and
  4. Robert Mustard
  1. Dep. of Biological Sciences, California State Univ., San Marcos, CA 92096


Semiarid chaparral and coastal sage shrublands of southern California have been exposed to high levels of atmospheric N for decades, which has the capacity to increase both N and C storage and cycling in these N-limited systems. Thus we hypothesize that soil C and N mineralization will be higher in areas that have been exposed to high atmospheric N deposition. This hypothesis was tested in a 50-wk laboratory incubation experiment where the inorganic N (NH4 + NO3) and CO2 production of chaparral and coastal sage soils were repeatedly measured. Soil was incubated in the dark at a constant temperature of 25°C and a soil moisture of 0.25 kg H2O kg−1 dry soil (65% water-filled pore space). Relative differences in N deposition exposure between the study sites were quantified by repeatedly rinsing and collecting the N accumulated on branch surfaces during 1 yr. Temporal trends in cumulative C and N mineralization were best described by single-pool first-order and zero-order models, respectively. Total N mineralization, but not C mineralization, increased linearly with relative N deposition, and NO3 accounted for 95% of the total inorganic N accumulated during the 50-wk incubation. The soil δ15N natural abundance increased with relative N deposition (r = 0.85, P < 0.05) and the soil C/N ratio declined with relative N deposition (r = −0.74, P < 0.05), suggesting that N deposition exposure enhanced N mineralization in part because of increases in the soil organic matter quality (i.e., lower C/N ratio). Furthermore, soil C storage declined as a function of relative N deposition exposure, indicating that high atmospheric N inputs are not likely to stimulate soil C storage in these semiarid ecosystems.

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