Soil nitrogen mineralization in a coastal fynbos succession

Abstract

Patterns of net nitrogen mineralization and nitrification in 0–7.5 cm deep mineral soils of different stages (seral ages 1, 6 and 20 years) of a post-fire coastal fynbos succession were assayed using laboratory andin situ incubations. No evidence of increasing allelopathic inhibition of nitrification with successional development was found as NO3−N was the predominant product at all seral stages and the NO3−N∶NH4−N ratio remained constant. Rather the results of field incubations of soils beneathProtea repens stands of different successional ages showed that increased mineralization and nitrification appeared to be associated with increased soil total N content rather than with successional age. Further, the incubation of soilsin situ during the dry summer months showed that NO3−N production appears to be closely related to temperature and soil moisture content, both of which are variables that vary throughout succession due to the changing structure of the vegetation.