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Abstract Changes in concentrations of ammonium-N and nitrate-N were determined at seven dates and most probable numbers of Nitrosomonas and Nitrobacter were determined at six dates from June 1975 to August 1976 in the 0-10 cm layer of soil from an old field, a 40-year-old pine stand, and a white oak-hickory stand near Durham, NC USA. As in previous studies, soils from forested ecosystems had consistently higher concentrations of ammonium and lower concentrations of nitrate and numbers of nitrifying bacteria than those of the old field. Consistent seasonal variations were observed in these various soil factors in all three vegetation types. Soil incubation experiments carried out in the lab at two dates indicated that the rates of nitrate production were highest in old field, intermediate in the hardwood, and lowest in the pine soils. Enrichment with ammonium stimulated nitrate production in nearly every case. Addition of CaCO 3 increased nitrate production in all soils, with highest rates being observed in hardwood soils. Variation between the two experiment dates were consistent with observed seasonal variations in the field. Addition of pine and hardwood ground litter extracts and whole leaf extracts to incubated soils had no observable effect on rates of nitrate production. The implications of these data with respect to current theories on the control of nitrification in forest ecosystems are discussed. Forest Sci. 25:287-297.
Montes et al. (Fri,) studied this question.