Factors Regulating Nitrification in Primary and Secondary Succession'

A six-point primary sere developed on sand dunes and a four-point secondary sere developed on old fields were studied to examine the regulation of nitrification in succession. Soils from sites along the seres were incubated in funnel-microlysimeters leached weekly with NH4CI and other nutrient solutions. Nitrate output in soils from the five youngest sites along the primary sere was rapidly stimulated by NH4+-N additions. Nitrification in soils from all four sites of the secondary sere was also stimulated by added ammonium. Added NH4+-N had no effect on the last primary sere site; in this site CaCO3 was the only treatment that stimulated potential nitrification. The possibility that labile inhibitors of nitrification were present in these sites was assessed by applying soil, litter, and whole-leaf washings, and whole-leaf and litter extracts to incubated soils. Soils amended with oxidizable carbon and pH-buffer solutions served as controls. Clear evidence for ecologically meaningful allelochemical inhibition of nitrification was found only in some subsites in the next-to-last site of the primary sere, which in previous incubations had had higher rates of nitrate production than any other site along this sere. No evidence for inhibition was found in the secondary sere. The effects of moisture and temperature on the rates of nitrification in these sites were also investigated. Results suggested that laboratory incubations may overestimate relative field rates of nitrification for early primary sere sites. Nitrification appears to be controlled by ammonium availability in at least the first four sites of the primary sere and perhaps the fifth. Allelochemical inhibition may also be important in this fifth site. A lag in nitrification that is counteracted by CaCO3 is an important regulator of nitrification in the last site. In the secondary sere NH4+-N availability appears to control nitrification in all sites.