Chemoautotrophic nitrification in acidic forest soils along an urban-to-rural transect

We studied N-mineralization and nitrification in oak forest soils along a 1 30 km urban-re-rural transect in the New York City metropolitan area. We fo und most urban and suburban stands had a substantial amount of extractable soil nitrate from July to December 1996, but nitrate pools in the rural sta nds were negligible. Lab incubations showed that urban and suburban soils n itrified rapidly, but the rural soils did not. Although soil pH was acidic in all stands, nitrification was totally inhibited by acetylene, indicating control of this process by chemoautotrophic rather than by heterotrophic m icrobes. When we amended soils with NH4+ or P, or raised their pH, nitrific ation in rural soils was not stimulated, nor was it further elevated in urb an soils. Raising pH did, however, increase NH4+ production in all soils. W e hypothesize that exotic earthworms, which are present in the urban and su burban stands but not in. the rural stands, may create soil conditions that favor autotrophic nitrifiers. (C) 1999 Elsevier Science Ltd. All rights re served.